Mark Cole, a senior BBC reporter, was one of those on board. Speaking live to Radio 4's The World at One, he described the scene as "utter chaos". After passing Reading the train "seemed to pick up speed and within seconds had left the track", he said.
"Glass was flying through the windows. The carriage I was in veered off. It caught fire. There was smoke everywhere. Obviously it broke into panic."
Mr Cole said he could see the other train in the wreckage - a goods train with yellow carriages. "It has certainly been hit by the InterCity train but it isn't clear whether it has ploughed into that on the line or actually just collided with that when it derailed."
He said the train had been "packed". In his carriage, there were no spare seats and some passengers were standing up.
Michael Hellier, 55, consultant physician, from Aldborne, Wiltshire, suffered cuts to his head and scalp and fears he might lose the sight of his right eye after he was thrown from his seat in a front carriage when the train crashed. He also suffered fractured ribs.
He said: "I was sitting in a front coach when there was suddenly a tremendous bang and everything went black. Something hit me very hard on the head which made me lose the vision in my right eye.
"I was thrown across the compartment as the coach rolled over, and my first thought was that I was dreaming, then I realised it was not a dream.
"As I fell, I broke some ribs on my left side. It was obvious that the carriage was still moving very fast.
"It all happened in about 15 to 20 seconds. I did not lose consciousness and as soon as the train stopped I was looking out of the hole where the window had been."
Manjit Singh, one of the first people at the scene, said he heard cries for help and comforted the driver of the InterCity train. "We heard the noise and went running down there," he said. "The driver was sitting shocked and stunned by the train. I grabbed him and asked him if he was all right. He said `What has happened?'
"He was all black from the smoke and his clothes were all dirty. The engine was on fire. From the second carriage there were cries of `Help, help, help'."
The disaster was best summed up by Dr Michael Rudolph, medical director of Ealing Hospital. He said: "The scene has been described to me as looking like a major aircraft disaster - carnage."
Despite the devastation, a relatively small number of people - as few as eight - were detained overnight in hospital. The rest were sent home after treatment.
A spokesman for the London Ambulance Service said some of the dead had been crushed by the enormous force of the impact. He added: "From such a horrific accident we have been very fortunate that the number of serious casualties is comparatively low. There is no one trapped at the scene."
Ealing Hospital, in west London, treated six men and five women. Joseph Gannon, general manager of Medicine, Accident and Emergency, said none of the casualties appeared to have life- threatening injuries. He added that three were being treated overnight, and two others could also be detained.
At the Central Middlesex Hospital six casualties were admitted. Four of them with minor injuries, including a 15-year-old boy, were released. Two others being kept overnight were a woman with a broken collar bone and suspected fractured pelvis, and a man with chest injuries.
Hillingdon Hospital received its first casualty just after 3pm and treated 10 people from the crash. Most of them had minor injuries.Reuse content