There was glass and debris everywhere and everyone was in a state of shock

British survivor Mark Oliver

He described the moment of impact: "The building violently lurched forward. Again it lurched forward."

He told the BBC: "I looked out of the window and saw the wreckage of the plane falling though I didn't know it was a plane then. There was a lot of fuel."

Calm evacuation

He told how most people remained calm as they attempted to escape through thick smoke and flames down 50 flights of stairs.

The twin towers collapsed within hours of the attack

The 34-year-old was separated from his colleagues in the confusion as he had to switch staircases.

"When we got there [the stairwell] it was engulfed in smoke and water and we were moved to a separate flight of stairs.

"We had to change again at about the 44th floor due to the smoke and I got separated from my colleagues."

"I had no idea where my colleagues were," he said.

Mr Oliver said: "I just headed down the stairs.

"As time went on I had to move to one side and let the injured pass.

"A lot of people were burnt, it was awful."

Once outside Mr Oliver, who had only been working in the building for three weeks, said he was greeted by a scene of pandemonium.

Panic stricken

"When we reached the subway, people were just screaming at us, 'Don't look up, just keep going, run for your lives'.

"There was glass and debris everywhere and everyone was in a state of shock," he said.

He said he was struck by the contrast between this act of incomprehensible violence and the selfless acts of others.

Mr Oliver said: "People were rushing to help people. People were doing everything they could to get people out."

His father Barry, from Northampton, said: "We tried non-stop to get through to him and it was wonderful when we heard his voice."

Safe and sound

A British banker told how he led 60 staff to safety moments before the World Trade Center collapsed.

Simon Perkins, 32, vice president of merchant bank Schroder Salomon Smith Barney, was on the 52nd floor of the building next to the twin towers when the attack happened.

His father Ray, from Plymouth, Devon, said: "When I heard about the attack I was convinced Simon had been killed and it was not for another four hours until I learned he was safe.

"We are very lucky that he is still alive.

"If he had been there when the planes struck he would have had no chance of getting out."

A telephone helpline has been set up for worried friends and relatives. For information call 0207 008 0000.