[The Duck]

Witnesses said the roof of the double-decker bus was blown into the sky outside the British Medical Association, near Tavistock Place.

One told BBC News 24 the front of the building had been "splattered with blood" and said there were sheets spread on the pavement.

Police said: "There have been further reports of multiple explosions."

Witness Belinda Seabrook said: "I was on the bus in front and heard an incredible bang, I turned round and half the double decker bus was in the air.

"It was a massive explosion and there were papers and half a bus flying through the air.

"There must be a lot of people dead as all the buses were packed, they had been turning people away from the Tube stops."

Another witness said police were about to conduct controlled explosions in the area. The area has been cordoned off.

There were unconfirmed reports there were other blasts on buses in South Kensington and in Marylebone.