Three large explosions have rocked a fuel depot near Hemel Hempstead in Hertfordshire shooting flames hundreds of feet into the sky.
Police say there are casualties and emergency services are at the scene.
The first blast happened at 0603 GMT at the Buncefield fuel depot, close to junction 8 of the M1 motorway, 10 miles from Luton airport.
It is being treated as an accident and rumours that a plane was involved are unfounded, said a police spokesman.
The M1 has been closed both ways between junctions 6a and 12.
Those living nearby have been evacuated.
Many houses have been damaged, with some reporting feeling effects from the explosion as far away as Oxfordshire, while it was heard in Surrey and Norfolk.
Eye witnesses reported buckled front doors, cracked walls and blown-out windows.
Witnesses said another two explosions followed the first at 0626 GMT and 0627 GMT.
The Buncefield depot is a major distribution terminal operated by Total and part-owned by Texaco, storing oil, petrol and well as kerosene which supplies Luton airport.
"We are doing everything we can to support the emergency services and to bring the situation under control," said a Total spokesman.
No further details were available, he added.
One eyewitness, Jonathan, told the BBC he was working a night shift in the building next door to the fuel depot at the time of the blast.
He received cuts and bruises.
He was sitting in his office "and the next minute I was on the floor and it was pitch black. I was thrown off my chair," he said.
He and a colleague had to break a window to get out because the doors were buckled, they got out of the front of the building and were taken to hospital by passing motorists.
BBC reporter Colin Campbell said: "There are huge fireballs gushing out of the fuel depot.
"Many people are standing by filming the scene on mobile phones. There are gigantic flames, it would be impossible to contain at the moment, it is out of control.
Plume of smoke after blast, scene from Luton
Police are describing it as a major incident
"It is a scene of utter devastation."
Malcolm Stewart, who drives a tanker at the terminal, said there were 20 tanks on the site, each holding three million gallons of fuel.
BBC correspondent Sinead Wilson, who lives in nearby St Albans said there was a huge plume of smoke covering the sky.
"There is a smell of gas, lots of fire engines, police cars in the area," she said.
"It looks to me as if the entire depot is under fire.
Eyewitness Sam Matton, who lives half a mile from the depot told BBC News: "The sky is sort of orange. The flames have got to be 60ft up in the air.
"The loft hatch in my house has actually fallen out, my neighbour's window has actually broken from the impact.
Dave Franklin told BBC News: "There was a massive loud bang which broke windows above us and to the right. The whole sky just turned orange and black."
Michael Vatty said: "The impression was that it was a clap of thunder, but as soon as we got up we saw the flames. We had the garage door blown in, the front door was also blown in."