At least 36 people were injured, two of them seriously, when a series of huge blasts ripped through an oil depot near Luton airport, northwest of London on Sunday, filling the sky with orange flames and thick black smoke and shattering windows and doors of nearby houses.
Detectives are treating the incident as an accident and earlier reports that a plane was involved in the blast are unfounded, police said.
"The fire is under control but there might still be more explosions," they said.
The first explosion took place at the Buncefield oil depot at Hertfordshire, close to the junction 8 of the motorway 20 km from Luton Airport, at 0603 GMT (1133 IST). Witnesses said two more explosions followed it at 0626 GMT (1156 IST) and 0627 GMT (1157 IST).
The blasts at the depot, operated by French firm Total and part-owned by American Texaco, could be heard up to 70 km away and flames shot more than 200 feet into the sky.
Hertfordshire police chief constable Frank Whiteley told newspersons, "All indications at this stage are that this was an accident. However, clearly we will keep open mind until we can confirm that for certain."
He said the explosions had caused some damage to buildings in the immediate vicinity.
Luton airport, which is used for budget and charter flights to destinations in Britain and abroad, is said to be operating as usual. A spokeswoman said no flights have been disrupted and the smoke was not affecting the flight path.
Howard Borkett-Jones, medical director of the West Hertfordshire Hospitals National Health Service Trust, said that a total of 36 people had been treated at the Hemel Hempstead general hospital for injuries from the explosions.
Of those, 34 had minor cuts and bruises, and all had been treated and discharged from the Accident and Emergency department.
One patient had been transferred to Watford general hospital for respiratory support and one had been admitted to the Hemel Hempstead General and was under observation.
The area is close to the M1 motorway linking London to north of England, a section of which was immediately closed.
In total, 20 petrol tanks are involved in the fire, each said to hold three million gallons of fuel, the BBC reported.
The area near the site has been evacuated, while police have advised residents living nearby to keep their windows and doors closed due to fumes.
The Buncefield depot is a major distribution terminal, storing oil, petrol as well as kerosene which supplies airports across the region, including Heathrow and Luton.
The country's fifth largest fuel distribution depot, it is also used by BP, Shell and British Pipeline.
Police said there was no indication the explosion would cause fuel shortages and warned against panic buying.
"We are doing everything we can to support the emergency services and to bring the situation under control," a spokesman for Total told the BBC.