Witnesses have described seeing one of Thursday's bombers in and around Shepherd's Bush Tube station.
Dozens of police were at the scene
Passenger Abisha Moyo believes he came face-to-face with the suspect, who later fled the scene.
He told the Daily Mail he was on the train when he heard a bang like a "pistol going off", and saw a fellow passenger lying on the floor.
He approached him and asked, "are you all right, mate?" but then saw the man was lying on top of a smoking rucksack.
The suspect then calmly left the rucksack behind, jumped on the tracks and walked away down the line.
When the bang was heard "some girls started screaming, the emergency cable was pulled and everyone started running away from him towards the front of the train," Mr Moyo said.
The blast happened at Shepherd's Bush Hammersmith and City line Tube station
An unnamed woman told BBC Two's Newsnight she saw a muscular black man in his twenties running away from the direction of the Hammersmith and City line Tube, crossing gardens and discarding a dirty shirt.
'Still shook up'
Local garage mechanic Rizgar Nash also said he saw a man running towards the nearby BBC Television Centre.
"I rushed to follow him, but he passed through Wood Lane and then to the BBC site, and then I just say leave him. I didn't know what was going on."
Police, while giving few details of what happened at Shepherd's Bush, did confirm a man tried to blow himself up.
Local residents were evacuated
The incident caused huge disruption in the area.
Hundreds of people were moved away from streets surrounding the station and shops were closed.
Some residents were unable to get to their homes and had to stay overnight in community centres.
Dozens of police officers were still at the Hammersmith and City line station on Friday morning. The station remained shut and some roads were also closed.
A passenger known only as Mo told the BBC News website he was also on the train, but on another carriage.
"I heard a bang, then there was smoke, people were panicking. I'm still a bit shook up from the whole ordeal. I saw everyone trying to get out of the train," he said.
Another passenger, Geoff Toley, said he was on his way back from the US when his train stopped a station short of Shepherd's Bush at Goldhawk Road.
"We were told that the current had gone out, then very shortly afterwards that we should evacuate the train and the station. People hurried but there was no panic at all.
Police have asked witnesses to come forward
A witness centre has been set up at Shepherd's Bush Hilton Hotel.
Or witnesses can phone 0800 789 321
"I then walked the short distance home... the London Underground staff got us out quickly and the police were there in large numbers quickly too."
Alex Okpongete was on the platform when there was an announcement ordering people to leave the station.
"Many people were panicking and couldn't believe this was actually happening. It was very shocking."
Police have asked witnesses to come forward. They have set up witness reception centre at Shepherd's Bush Hilton Hotel in Kensington.
Shepherd's Bush has two Tube stations, about 400m apart. They do not share any lines and the Central line station was unaffected.
Anyone with any information can also phone the anti-terrorist hotline on 0800 789 321.