A big fire at a warehouse sent out a pall of black smoke over east London on Monday, but there were no reports of casualties and police said there was nothing to suggest it was anything more than a fire.
Fifteen fire engines and 75 firefighters rushed to the scene of the blaze at an industrial estate in the Stratford area of east London, the London fire brigade said.
A security official said the blaze was at an old bus depot, not far from the planned site of the athletes' village for the 2012 London Olympic Games.
Two ambulances went to the scene but the London ambulance service said no casualties had been reported.
British media reported that an explosion had been heard, raising fears of a possible attack.
But a police spokesman said: "We've got nothing to suggest that it is anything other than a fire at the moment."
"At the moment we're monitoring what's going on. We're in close discussion with the Met (London's Metropolitan Police)," a spokesman for the Home Office (interior ministry) said. "'No reports of an explosion' is what they've said to us."
Asked if it was possible to rule out any terrorist connection, a security source said: "We wouldn't rule anything out at this stage, its too early. But for the time being it's being responded to as a fire.
"Obviously it's something that we will be keeping an eye on. We're not going to rule anything out this early in the day."
Suicide bombers killed 52 people in July 7, 2005 attacks on London's transport system.