LONDON, England (CNN) -- Several large explosions at a fuel depot have shaken a town north of London, lighting up the predawn sky, ighting up the predawn sky, injuring at least 36 people and sparking a massive blaze.
"All indications are, at this stage, that this was an accident," Hertfordshire Chief Constable Frank Whiteley said on Sunday. "However, clearly we will keep an open mind ... until we can confirm that for certain."
Four people were seriously injured, he said, but the majority were "walking casualties" and were being treated at local hospitals.
It was too early, Whiteley said, to determine the cause of the explosions.
Officials at the Luton Airport told British television network ITN the blast did not involve an aircraft -- despite some earlier reports Sunday -- and was not on airport grounds. Hertfordshire police also said there was no plane involved.
Britain has been on edge for attacks since four suicide bombers killed 52 commuters in July on London's transport system, but the police statement appeared to rule out any attack.
Although firefighting units were on the scene, authorities said the fire may have to burn itself out. "It could go into days," Roy Wilsher, fire department spokesman, told reporters. He described the fire as "the largest I've seen." Authorities said the blaze was under control, however, and was not expected to spread.
"What we're really concerned about is toxic smoke from the area," Vine told CNN. "There's a heavy cloud. We don't know if it's toxic, but we're asking people in Hemel Hempstead to keep their windows and doors closed and stay inside."
The smoke was drifting slowly east, Whiteley said.
Strange taste
Residents closest to the depot were being evacuated, she said, and nearby roads, including the M1 and M10, were closed. "What we really want is for people to keep away from the area."
Nearby residents left quickly, some throwing possessions in the backs of their cars. Whiteley said those with doors and windows damaged by the blasts should leave.
Further explosions were expected, Whiteley said, as intact tanks were threatened by the flames. However, Whiteley said those blasts should not be as large as the first ones, which involved some main tanks. About 150,000 tons of various types of fuel are stored there, authorities said.
Hemel Hempstead residents reported hearing a loud boom about 6 a.m. local time. Two other blasts followed, British television network ITN reported, at 6:26 and 6:27 a.m.
The network showed flames shooting an estimated 80 to 100 meters (up to 300 feet) in the air, along with an immense cloud of smoke blocking out the sun. Witnesses told ITN the blasts shattered windows and caused other damage at nearby homes.
As the smoke spread across Hemel Hempstead, witnesses said there was a strange taste in the air.
"It's a horrible feeling in the back of your throat," Andy Dicker told the network. "Very unpleasant."
At least one of the blasts was enough to wake residents of west London.
Video from the scene showed heavy damage to buildings at the depot and nearby roads covered in debris from the blasts.
Witness Simon Heyward described to ITN seeing "what looked like fireworks shooting up into the sky." Police, he said, had cordoned off the area.
Another woman said she thought the noise was an earthquake or a plane crash at the Luton Airport. "It was that kind of intense noise," she said.
Texaco owns 40 percent of Buncefield, but does not operate the facility. The other 60 percent is owned by Total, according to Texaco-Chevron UK and U.S.-based Texaco. No American workers were at the site, a Texaco USA spokesman said. Although the terminal is the fifth-largest in Britain, Whiteley told reporters there should be no concern about a fuel shortage.
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