A spokesman for Hertfordshire Fire and Rescue said nobody was thought to have been injured.
The service, which has taken more than 70 calls about the blaze, has asked people to avoid the area and keep windows closed.
Paul Kirby/BBC
Mr Cunningham, who lives nearby, said: "I just heard an unbelievable noise that sounded like a jet and when I looked out my window, one of the buses exploded in a ball of flames."
People reported on Twitter that the smoke could be seen in St Albans, about 11 miles (18km) away.
Paul Kirby/BBC
Paul Kirby, a BBC reporter who saw the fire, said he spoke to bus drivers who told him they were relieved the underground diesel storage appeared to be safe.
It is thought that up to seven hybrid buses had gone up in flames and "you could hear several loud bangs which they said were tyres" he said.
Workers managed to move some buses but not all as they were at risk of fire, Mr Kirby added.
Police are investigating claims that a van driver "crushed" three ducklings by mowing them down as they were crossing the road.
Staffordshire Police said officers were made aware of the incident, which took place in Trentham, a southern suburb of Stoke-on-Trent, on Friday.
Images of the ducklings laying in the road were shared across social media after being posted on Facebook by a man called Steven Walley.
He said other drivers stopped to let the family of seven ducklings cross, but the driver of a white van "could not wait" and instead "drove straight over them".
Mr Walley wrote: "I've just been driving on the A34 at Trentham Gardens roundabout when a family of seven ducklings were crossing the road.
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"All the traffic stopped to let them cross but disgustingly this van driver, after initially stopping, could not then wait for the five seconds it would have taken to let them cross and drove straight over them, crushing three of them."
Mr Walley added he followed the vehicle to a nearby lay-by and had what he described as a "very heated conversation" with the van driver.
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Staffordshire Police acknowledged the incident was an "emotive issue" and advised people not to "take matters into their own hands".
The police said in a statement: "We are aware of a post circulating of a van driver who is believed to have killed ducklings in Trentham.
"We have made contact with the author of the post and are establishing potential offences under the Wildlife and Countryside Act.
"We understand this is an emotive issue for many people and we ask please that you do not take matters into your own hands."
Events are being held to mark the fifth anniversary of the Manchester Arena terror attack.
Twenty-two people died when a suicide bomber blew himself up outside an Ariana Grande concert on 22 May 2017.
Among the tributes, a minute's applause will be held at the start of each wave of runners taking part in the annual Great Manchester Run.
Blast survivor Freya Lewis, who is starting and taking part in the race, said she was "nervous but excited".
The 19-year-old has learned to walk again after being injured in the explosion, which killed her best friend Nell Jones.
"Nell was such a massive part of my life, and to have her not part of it is still so odd," she said.
"I'm definitely on my way to healing and I think I still keep the memory of her alive in everything I do."
PA Media
Throughout the day, people can pay respects at the new Glade of Light memorial, which was officially opened by the Duke and Duchess of Cambridge earlier this month.
The names of the 22 victims will be read out at Victoria Station, which is next to the arena, and at Manchester Cathedral.
The cathedral's bells will also toll at 22:31 BST, marking the moment of the attack.
Manchester City Council leader Bev Craig said the 2017 Great Manchester Run - held six days after the attack - showed "love proved stronger".
"We will never forget those whose lives were so cruelly taken, or those whose lives were changed forever that day.
"But nor should we forget the remarkable spirit shown in the aftermath of the attack as the city came together in solidarity, compassion and a refusal to give in to hatred and fear."
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Suicide bomber Salman Abedi, who was born in the city, also injured hundreds of people when he detonated a homemade device after the concert.
An independent public inquiry on the attack recently ended after hearing evidence from 267 witnesses since September 2020.
Its reports on the actions of the emergency services and whether security agencies could have stopped the bombing are due to be published later this year.
Why not follow BBC North West on Facebook, Twitter and Instagram? You can also send story ideas to northwest.newsonline@bbc.co.uk
A former Conservative leader has called for benefits to be immediately increased to help the poorest cope with the cost of living.
But Sir Iain Duncan Smith's plea came as two cabinet ministers spoke out publicly against bringing in a windfall tax on oil and gas companies to help pay for support for people struggling.
In an interview with the Sunday Telegraph, Northern Ireland Secretary Brandon Lewis said it would "put off investment" while Health Secretary Sajid Javid told Conservative activists in Wales he instinctively didn't like it.
Chancellor Rishi Sunak has refused to rule out the idea, with one newspaper on Sunday reporting a staggered version of the levy is being looked at.
Sir Iain had told Sky News there should also be tax cuts for those in work to help "the squeezed middle".
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He said: "During the course of this spike we should make sure we bring those benefits that are relevant to those people who are in need up to be able to afford to pay bills that are going to be higher."
Universal credit and other benefits rose by 3.1% last month, in line with the CPI rate of inflation in September last year.
Amid spiralling prices, the government is under pressure to take further action with splits over the potential to raise money through a 'windfall tax' on the profits of oil and gas companies.
The Sunday Times has reported the chancellor is "attracted" by the idea of a "pro-investment" form of the levy which would offer different rates of tax depending on how much a company was prepared to invest in the UK.
Image:Former leader of the Conservative Party Iain Duncan Smith. Pic: AP
A Treasury source pointed to previous comments made by Mr Sunak in which he said no options were off the table provided they lead to "significant investment back into the UK economy" and support "energy security".
Former Tory minister John Redwood has previously told Sky News "Labour's windfall tax" was not needed because North Sea oil and gas "already pays double tax".
He called on the Treasury to use increased VAT receipts to raise benefits and cut broader tax rates.
Another former minister said the "gut instinct" for many in the Conservative party would be to help people through tax cuts but also acknowledged that "may be turned on its head" given the direct interventions that had taken place during the pandemic.
A newer intake MP said he had sympathy for the idea of increasing benefits but said that could only happen "if economy is strong enough to pay for it" and added that won't happen "if we have taxed it to death".
The government is already handing out £150 council tax rebates for many homes and will take £200 off energy bills from October.
Sir Iain's comments come as the think tank he founded - the Centre for Social Justice - called for benefit rates to be reviewed quarterly rather than annually and for tax cuts to be implemented for working people who claim Universal Credit.
Last week the chancellor said he was not able to raise the payments more than 3.1% due to an old computer system that the Department for Work and Pensions uses.
The Institute for Fiscal Studies economic think tank has suggested the poorest households might be facing inflation of 10.9%.
This is higher than average because they spend a larger portion of their money on heating and lighting their homes.
A Treasury source pointed to previous comments made by Mr Sunak in which he said he was "ready to do more" and that he was "learning more" about what was going on in the economy every week.
These include introducing a new offence of obstructing major transport networks, which carries a maximum penalty of six months' imprisonment, an unlimited fine or both.
Interfering with key national infrastructure - such as railways, roads and printing presses - will also become a criminal offence, which would bring a penalty of up to 12 months' imprisonment, an unlimited fine, or both.
Amnesty International says the home secretary is smearing peaceful protest with the plans, while Fair Trials says the government "appears to be intent on destroying the right to peaceful protest rather than protecting it".
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As she opens the second reading debate on the bill in the House of Commons on Monday, Ms Patel is expected to tell MPs: "From day one, this government has put the safety and interests of the law-abiding majority first... but recently we have seen a rise in criminal, disruptive, and self-defeating tactics - from a supremely selfish minority.
"Their actions divert police resources away from the communities where they are needed most... and we are seeing parts of the country grind to a halt... This is reprehensible behaviour and I will not tolerate it."
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As part of the bill, police will also be given the power to proactively stop and search people to seize items intended for "locking-on" purposes, such as glue or bamboo structures meant for obstructing police.
'Lock-on' tactics, such as protesters gluing themselves to roads or public transport, have been repeatedly employed by groups such as Insulate Britain and Just Stop Oil.
Courts will also be given new powers to make Serious Disruption Prevention Orders, which would make those who have been found to repeatedly cause disruption wear an electronic tag, to ensure they are not in a particular place where they might commit a "protest-related offence".
Ms Patel will add: "I will not stand by and let anti-social individuals keep causing misery and chaos for others. The Public Order Bill will empower the police to take more proactive action to protect the rights of the public to go about their lives in peace.
"However passionately one believes in a cause, we do not make policy through mob rule in this country... I will not be deterred from backing the police and standing up for the law-abiding majority, and that's what the Public Order Bill does."
But Labour's shadow home secretary Yvette Cooper said the bill "fails on every count".
She said it was too "widely drawn," and could also penalise passers-by or peaceful protesters.
She said Labour's suggestion to make it quicker to secure injunctions when vital services are threatened with disruption, would be better.
"This is a wasted opportunity to take a sensible approach and is getting things all wrong.
"The home secretary is just recycling widely drawn measures from the Police Bill which have already been rejected by parliament.
"Tomorrow we should instead be having the second reading of the long-awaited Victims Bill with measures to tackle rising crime and falling prosecutions; instead, the home secretary is letting everyone down."
Amnesty International UK's head of policy and government affairs Allan Hogarth described it as "outrageous" for Ms Patel to "smear peaceful protesters as a 'mob'".
Image:Protests in Hong Kong were hailed by the UK government
She added: "At a time when protesters in places like Moscow or Hong Kong are hailed for their bravery - including by members of our government - it's incredibly depressing that Priti Patel is pushing these repressive laws."
Norman Reimer, the chief executive of the group Fair Trials, had said of the home secretary's latest proposals: "By reintroducing plans that have already been rejected by UK parliamentarians, the UK government appears to be intent on destroying the right to peaceful protest rather than protecting it."
Meanwhile, Extinction Rebellion (XR) has already announced plans to "bring millions of people on to the streets" in response to the new bill after it was announced in the Queen's Speech earlier this month.
Five people were injured, two seriously, when parts of two spectator stands collapsed at a Trooping the Colour rehearsal at Horse Guards Parade in central London.
The Army said one stand gave way just before 11:00 BST and part of a second stand collapsed a short time later.
London Ambulance Service (LAS) said two patients were taken to major trauma units as a priority.
Three others were treated at the scene with one later transferred to hospital.
Spectators were evacuated from the stands by the Army and police so safety checks could be carried out.
A "partial structural failure" was to blame, the Army said. LAS has not confirmed the severity of the injuries that were sustained.
Marcus Dell
Marcus Dell, who was at the event, said he heard screams.
"Everyone had stood for the national anthem and there was a bit of a commotion. The first we heard was that one of floorboards had broken and someone had fallen through and hurt themselves.
"There was a lot of chatter in the stands and a few people did leave."
He said a floorboard had cracked behind him and then about 25 minutes later, there was a similar incident in the stand opposite.
When the area was evacuated as a safety precaution there was confusion, Mr Dell said, although the "police did a good job of making sure there wasn't any panic".
Paul Rogers, who was nearby, said: "We heard a loud bang and a scream and a person shouting 'Help! Help!'
"A number of people climbed over the back wall and went below the section of stand that had broken. It lasted about 20 minutes.
"It just seemed like a small section of the stand went," Mr Rogers said.
Another witness said the stands were emptied one by one, adding that the evacuation was "very well organised, not chaos as quoted by some".
What is Trooping the Colour?
It's a parade which has marked the official birthday of the British sovereign
It has been held for more than 260 years
Last year's parade was in the grounds of Windsor Castle, rather than in central London
It is normally held on the Queen's official birthday which is marked on the second Saturday of June each year
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To play this video you need to enable JavaScript in your browser.
Up to 1,450 soldiers from the Household Division and the King's Troop Royal Horse Artillery were taking part in the parade, alongside about 400 musicians from the Massed Bands.
It is very similar to the Trooping the Colour event reviewed annually by the Queen - she is due to do so on 2 June as part of the Jubilee celebrations. Prince William is to review the troops next Saturday.
Earlier, the troops were being reviewed by Maj Gen Christopher Ghika of the Household Division.
An LAS spokesperson said: "We sent a tactical response unit, an ambulance crew, two cycle responders and an incident response officer.
"We worked alongside St John Ambulance volunteers to treat five people at the scene. We took one patient to a major trauma centre as a priority. St John Ambulance took a second patient to a major trauma centre as a priority. We discharged three patients at the scene. We later arranged transport to hospital for one of these patients."
In a statement, the Army said: "Safety is our number-one priority and we are urgently working with our partners and relevant organisations to understand what happened and make sure it doesn't happen again."
Two people have been taken to hospital after part of a stand collapsed at a Trooping the Colour rehearsal at Horse Guards Parade in central London.
The Army said two parts of the spectator stands collapsed just before 11:00 BST.
London Ambulance Service (LAS) said two patients were taken to a major trauma unit as a priority.
The remaining crowds were evacuated from the stands by the Army and police so safety checks could be carried out.
The injuries happened when one of the stands suffered a "partial structural failure", the Army said.
LAS has not confirmed the severity of the injuries that were sustained.
Marcus Dell
Marcus Dell, who was at the event, said he heard screams.
"Everyone had stood for the national anthem and there was a bit of a commotion. The first we heard was that one of floorboards had broken and someone had fallen through and hurt themselves.
"There was a lot of chatter in the stands and a few people did leave."
He said a floorboard had cracked behind him and then about 25 minutes later, there was a similar incident in the stand opposite.
Mr Dell said when the area was evacuated as a safety precaution, there was confusion, however the "police did a good job of making sure there wasn't any panic".
Paul Rogers, who was near the stand, said: "We heard a loud bang and a scream and a person shouting 'Help! Help!'.
"A number of people climbed over the back wall and went below the section of stand that had broken. It lasted about 20 minutes.
"It just seemed like a small section of the stand went," Mr Rogers said.
Another witness said the stands were emptied one by one, adding that the evacuation was "very well organised, not chaos as quoted by some".
What is Trooping the Colour?
It's a parade which has marked the official birthday of the British sovereign
It has been held for more than 260 years
Last year's parade was held in the grounds of Windsor Castle, rather than in central London
It is normally held on the Queen's official birthday which is marked on the second Saturday of June each year
This video can not be played
To play this video you need to enable JavaScript in your browser.
Up to 1,450 soldiers from the Household Division and the King's Troop Royal Horse Artillery were taking part in the parade, alongside about 400 musicians from the Massed Bands.
It is very similar to the Trooping the Colour event reviewed annually by the Queen - she is due to do so on 2 June as part of the Jubilee celebrations. Prince William is to review the troops next Saturday.
Earlier, the troops were being reviewed by Maj Gen Christopher Ghika of the Household Division.
An LAS spokesperson said: "We sent a tactical response unit, an ambulance crew, two cycle responders and an incident response officer.
"We worked alongside St John Ambulance volunteers to treat five people at the scene. We took one patient to a major trauma centre as a priority. St John Ambulance took a second patient to a major trauma centre as a priority. We discharged three patients at the scene. We later arranged transport to hospital for one of these patients."
In a statement, the Army said: "Safety is our number-one priority and we are urgently working with our partners and relevant organisations to understand what happened and make sure it doesn't happen again."
