The death toll could rise further as an unspecified number of bodies have still to be recovered from the wreckage, said British Transport Police.

Carriages came off the track and one train burst into flames. A massive column of smoke could be seen across west London.

Ambulances have taken 127 people to hospitals in and around west London, many with burns injuries. St Mary's Hospital in Paddington cancelled all out-patient appointments to treat the majority of the wounded.

Twenty-one people were seriously injured. A London Ambulance Service spokesman said: "Of those injured, some of the patients are extremely critical and are suffering from life-threatening injuries."

The BBC's Daniel Boettcher: "The search for bodies continues"

Some survivors were trapped for several hours in one of the carriages, but all of them are now reported to have been freed. Firefighters are continuing to look for bodies in the wreckage.

The walking wounded were treated at a school and a supermarket near the scene. Among the injured was writer Jilly Cooper, who crawled to safety through a window and is not believed to be seriously hurt.

The accident happened near Ladroke Grove in west London at 0811BST, on the same stretch of line as the Southall rail crash in 1997 in which seven people died and 150 were injured.

The 0806BST two-carriage service run by Thames Trains from Paddington to Bedwyn in Wiltshire collided with the incoming 0603BST Great Western 125 express train from Cheltenham.

The BBC's George Eykyn: "The rescue has been officially declared completed"

Mark Rogers, a passenger on one of the trains, said: "There was an almighty crash and the train rolled over and over, first onto its roof and then onto its side.

"One woman I saw thrown out of the window and she was trapped beneath the train. She was at least very severely injured."

Click here to see the site of the crash

Mr Rogers said the carriage behind the driver had been "ripped apart like a sardine can" and was lying over the top of the 125.

Another survivor, Patrick Welcome, was involved in a plane crash just two weeks ago when the jet in which he was travelling overshot a runway and collided with trees in Bangkok. "My guardian angels have been working overtime," he said.

Survivor Phil Longman describes the crash scene

Andrew McNaughton, of Railtrack, told reporters from the position of the track it "must have been very near to a head-on collision".

He said there would have been about 4-500 passengers on the express train, with more than 150 people on the Thames train. The casualties were in the front carriages of the 125 and on the smaller train.

There was a standard automatic warning system on both trains, but Mr McNaughton would not confirm whether the systems were switched on or off.

Up to 30 ambulances raced to the scene

Health and Safety Executive inspectors have begun an investigation at the crash scene.

The Transport Secretary John Prescott has announced that there will be a public inquiry into the crash, while the Prime Minister, Tony Blair, said he was "appalled by what is a truly dreadful tragedy".

Lawyers for the victims of the Southall rail crash said they would demand that the inquiry into the 1997 disaster expand to cover Tuesday's crash.

And Conservative Transport spokesman John Redwood said: "We need a proper inquiry and we need some answers for the future."

The Queen has sent a message of sympathy to those bereaved and injured.

"Please pass on my sympathies to the families and friends of those who have died, and to those who have been injured.

"Could you also express my thanks to those members of the rail and emergency services who are still working to help those hurt or in shock."

Emergency numbers for worried relatives and friends are 0207 834 7777 and 01793 499458.

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