Several huge explosions rocked a major fuel depot northwest of London on Sunday morning, injuring at least 43 people, forcing the evacuation of hundreds more and creating a massive cloud of black smoke that darkened a sunny winter sky over much of southeastern England.

"This is possibly the largest incident of its kind in peacetime Europe," Roy Wilsher, the chief fire officer of Hertfordshire county, told reporters.

At least three explosions just after 6 a.m., which could be heard more than 100 miles away, resulted in a fire that officials said could burn for at least another day and caused shutdowns of the M1, one of Britain's busiest highways.

The blasts knocked out windows around the site and shook homes and woke people across London. Officials said several flights at Heathrow Airport were delayed by the heavy smoke in the area; no delays were reported at Luton airport, which is closer to the explosion.

"All indications at this stage are that this was an accident. However, clearly we will keep an open mind until we can confirm that for certain," Hertfordshire Police Chief Frank Whiteley told reporters.

Police said the fire at the Buncefield fuel depot in the Hemel Hempstead area of Hertfordshire, about 25 miles northwest of central London, involved at least 20 gasoline storage tanks that each hold 3 million gallons of fuel. The depot is a major distribution terminal operated by Total, part-owned by Texaco and also used by BP and Shell. The companies store oil, gasoline, kerosene and aviation fuel in large tanks.

Hertfordshire police issued a warning to residents to keep their windows and doors closed as the cloud of thick smoke, clearly visible on satellite photos, drifted east. Police said there was "nothing to suggest the cloud is toxic" but urged residents to stay indoors as a precaution. People also were urged to refrain from panic buying of gasoline.

Police said two people were seriously injured and hospitalized and 41 others were treated in hospitals for minor injuries.

"It was awful, it was like we were in hell. The flames were 200 feet high," Raheel Ashraf, a part-time security guard in an office building adjacent to the depot, told the BBC. Ashraf said he was doing final checks on the night shift when he smelled a heavy odor of fuel. Moments later, he told the network, he heard a "humongous explosion."

"I opened my eyes and there was nothing left of the building," said Ashraf, who escaped with just scratches. "I was crunched into a ball, looking around, wondering if I was asleep. All the walls, everything, was just shattered. There was no light in there but I could see the sky."

Smoke fills the sky near Hemel Hempstead after explosions at a fuel depot. Police said the fire involved at least 20 fuel tanks that each hold 3 million gallons.

A child and his dog watch the aftermath of the explosions that left two people still hospitalized and forced the evacuation of hundreds of others.