From Sky news http://www.sky.com/skynews/article/0,,30000-1188273,00.html
SURVIVORS DESCRIBE EXPLOSIONS
Passengers involved in the Metropolitan Line explosion are reported to have attempted to smash the windows of their Tube carriages with umbrellas in an attempt to escape.
Another witness told Sky News there was an explosion at the back of a Tube carriage and he had seen bodies.
Police are thought to have been sent into tunnels to evacuate people along the tracks.
Bradley Anderson told Sky News that he was involved in the Edgware Road incident on a Circle line train.
He said: "We just left Paddington station. About 15 seconds later there was some kind of explosion and we collided with another train.
"We were heading into the station when there was some kind of explosion or something.
"Everything went black and we collided into some kind of oncoming train.
"There was debris all over the trains. They evacuated us."
Clare Benson, 33, a city banker from Kensington, was on a tube at Edware Road when she heard a massive explosion in the tunnel behind her.
It was about 8.40am.
"I was in the last carriage at the back of the train nearest the tunnel when I heard a huge bang - you could feel it.
"The lights went off for a couple of minutes and people were scared and wondering what to do.
"The drivers got out and were looking into the tunnel, then they announced that we should evacuate.
"My ears are still ringing and I was shaking."
One witess told Sky there was an explosion at the back of a tube carriage.
"There was a big hole in the carriage. There were people lying everywhere covered in blood," he said.
"People were screaming. We could not get out.
"The explosion was at the back of the carriage."
He said people managed to walk through the carriages to get out.
He said there was "bodies lying everywhere".
BLASTS ON TUBES AND BUS
According to reports a bus has exploded in central London just minutes after a number of blasts on London's Underground.
"I saw lots of people running up a road and then saw the top of a bus destroyed," one eyewitness told Sky News.
Sky News producer Bob Mills said he heard the loud explosion near Euston Station.
Scotland Yard could not confirm reports of an explosion on a bus in Russell Square. A spokeswoman said police were at the scene and attempting to determine what had happened.
The entire Tube network has been shut down following the blasts at Aldgate, Edgware Road, King's Cross, Old Street and Russell Square.
More at http://www.sky.com/skynews/article/0,,30000-1188265,00.html
"Everything went black and we collided into some kind of oncoming train.
"There was debris all over the trains. They evacuated us."
If a bomb, it sounds like it blew at least one of the trains clear off of its track.