'Large flash of light'

Eyewitnesses of the blast have been describing how cars shook and a large flash of light came from the MI6 building.

James Trott told BBC News 24: "A friend of mine was on a bus and he was coming over the bridge and heard two big explosions and glass shattered all over the place.

"The next thing we knew there were about six fire engines coming up the road and police were blocking all the roads off.

The ground seemed to shake and my car was shaking

Eyewitness Andrew Preece

"They have got Vauxhall Bridge completely blocked off. There's no cars coming down here at all."

BBC News Online journalist Justin Pearce, near the area at the time of the explosion, said he definitely heard two blasts.

"There were two bangs, two seconds apart," he said.

Another eyewitness, Andrew Preece, reported seeing a flash of light coming from the MI6 building itself.

He said: "I was approaching Vauxhall Bridge from the south side. I saw a large flash of light coming from the top of the building which was followed by a large bang.

"The ground seemed to shake and my car was shaking. I was a bit shocked."

Andrew Preece was driving his girlfriend home

Sridharan Balakrishnn, 23, who works at the Texaco garage on the Albert Embankment behind the building, also reported hearing "two large bangs".

"It was very loud and hurt my ears. Then I saw smoke coming from the MI6 building.

"I was very scared and I went into the office at the back of the garage and phoned my manager to ask him what to do.

"I didn't call the police because they were here so quickly - it took around five to 10 minutes.

'Two explosions'

"There were two vans and two car loads. Then an ambulance came. "I didn't see anyone being carried out of the building."

Eyewitness Alex Frank, who lives close to the building, said he heard two distinct explosions.

"There were definitely two explosions of the same strength. They were loud enough to shake the building I'm living in."

Local resident Wendy Cook, a barrister, said there were two large explosions, "exceptionally loud, one running into the other.

They rattled my windows. It was obviously a really serious explosion."

She added there was then total silence and no sign of flames or fire.

"If it is a bomb I am amazed that anyone could have got so close to the security services building or into it."

Asked how she felt about living within yards of the MI6 headquarters, Miss Cook said: "On the whole it makes you feel safer because of the local security it affords you."