Arash Kazerouni, 22, said: "There was a loud bang and the train ground to a halt. People started panicking, screaming and crying as smoke came into the carriage.
"A man told everyone to be calm and we were led to safety along the track."
Mr Kazerouni, from Edmonton, North London, who works for Barnet Council as a trading standards administrative officer, was heading from Liverpool Street to Cannon Street for a job interview in IT support.
He said: "Everyone was terrified when it happened.
"When they led us to safety, I went past the carriage where I think the explosion was. It was the second one from the front.
"The metal was all blown outwards and there were people inside being helped by paramedics.
"One guy was being tended outside on the track. His clothes were torn off and he seemed pretty badly burned.
"This whole thing teaches you, appreciate your life, you don't know what's round the corner."
Police sealed off several streets around Aldgate and told people to stand back as ambulances were bringing out casualties.
Sarah Reid, 23, a student doing work experience, was on the carriage next door to the one which was struck by the explosion.
Speaking after the ordeal, having been led out down the track, near Liverpool Street station, she told how she saw a carriage ripped apart with the roof blown off.
"I think some people may have died," she said.
The blast had pulled some people's clothes off.
She added: "I was on the train and there was a fire outside the carriage window and then there was a sudden jolt which shook us forward.
"The explosion was behind me.
"Some people took charge. We went out of the back of the carriage."
She said the explosion happened at 8.50am but she was not able to get off the carriage until 9.30am.
Miss Reid said an announcement came on but cut off after saying: "Hello".
"There was really hard banging from the carriage next door to us," she said, describing events immediately after the blast.
"That was where it happened," she added.
She said there was a fire which she had seen initially outside the window of her carriage.
Describing being led away from the scene, she said: "A carriage was split in two, all jagged, and without a roof, just open.
"I saw bodies, I think."Reuse content