The first sign that something was wrong was the smell.
As the northbound Victoria line train approached Warren Street the carriage filled with a stench like burning rubber.
Some kind of device had exploded in one of the carriages, sending the 20 or so passengers scattering in panic.
Ebeena Adofa, sitting a few carriages from the explosion, had no idea what was going on until panicked passengers burst through the connecting doors. "People ran into my carriage. I could smell burning. We pulled into the station. When we got off the train people were screaming. There was just confusion."
Caroline Russell was caught in the crush as people tried to get out. "When we got to the station the doors opened and people looked at each other. Then there was a stampede of people from the front of the train.
"A young Italian girl collapsed at my feet. I helped her up and out of the station which is very deep. I sat her down outside the station and a boy came and sat down next to her.
"He said he had seen a guy's rucksack explode; he was an English guy, he had a rucksack and it seemed to explode like a firework, not a bomb."
Lawrence Wahlund, 43, unaware of the chaos below, was heading down the escalator just as panic-stricken people spilt off the train. He found a sudden surge of commuters pushing up towards him.
"At first people were pushing to keep going down, thinking there was a fault with the escalator. Then someone shouted 'Get out!' and everyone turned to run.
"I just saw people rushing up. People were running up the escalator but then the escalator was stopped so we had to run up too.
"One thing we realised pretty soon was the police were walking around looking among the people outside the station. We got the idea and other people got the idea that they were probably looking for someone in the crowd and that made us feel even more uncomfortable. I saw the police taking photographs of everyone around."
Arnold Wright, 43, a New Yorker who lived through the 11 September 2001 attacks and recently moved to London, was stepping into the entrance of Warren Street just as police arrived.
"The gates were slammed shut in front of me. Police with dogs were pushing into the station and more police were photographing everyone coming out. There were people everywhere. It's like 9/11 all over.
"My family have been ringing me, everyone's very scared."
Within minutes, scores of police had cordoned off Tottenham Court Road and Euston Road in both directions.
Hundreds of onlookers, many evacuated from their places of work, pushed at the barrier to get a closer look.
Police worked their way through the lunchtime crowds clearing bemused drinkers from the pubs, pints in their hands, and closing coffee bars with the staff still inside, trapped within the cordon.
Michelle Sinclair, 24, was sitting in a restaurant near Warren Street Tube when police started sealing off the area. She said two British Transport Police took away a man in their car.
"We saw police go into the station and later they were searching the bag of a man who got into the back of their unmarked car. There was no struggling and he got into the car by himself and he wasn't handcuffed."
Ms Sinclair said the man was tanned, with long, dark hair and was carrying a red rucksack.
Crowds of confused office workers on their lunch break found themselves stopped and searched as the police operation got under way.
Ahmed Laarbi, 29, says he was walking near Warren Street Tube station at about 2.10pm when he was stopped and searched.
"I was trying to go to my job as a cleaner at Victoria station," he said. "The police asked me what's in your bag, what are you doing here. They asked me what my name was, where I lived, what my job was. They looked in my bag, in my trousers, everything."
Mr Laarbi, a Muslim from Morocco who lives in Stamford Hill, north London, said he was not angry.
"They're just doing their job," he said. "But this is my city too. I have an English girlfriend and friends."
- INDEPENDENT
Screams as Tube passengers stampede
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