Mark Whitby said: "I was sitting on the train... I heard a load of noise, people saying, 'Get out, get down'.
"I saw an Asian guy. He ran on to the train, he was hotly pursued by three plain clothes officers, one of them was wielding a black handgun.
"He half tripped... they pushed him to the floor and basically unloaded five shots into him," he told BBC News 24.
"As [the suspect] got onto the train I looked at his face, he looked sort of left and right, but he basically looked like a cornered rabbit, a cornered fox.
"He looked absolutely petrified and then he sort of tripped, but they were hotly pursuing him, [they] couldn't have been any more than two or three feet behind him at this time and he half tripped and was half pushed to the floor and the policeman nearest to me had the black automatic pistol in his left hand.
"He held it down to the guy and unloaded five shots into him.
"He [the suspect] had a baseball cap on and quite a sort of thickish coat - it was a coat you'd wear in winter, sort of like a padded jacket.
"He might have had something concealed under there, I don't know. But it looked sort of out of place with the sort of weather we've been having, the sort of hot humid weather.
Commuter Anthony Larkin, who was also on the train at Stockwell station, told 5 Live he saw police chasing a man.
"I saw these police officers in uniform and out of uniform shouting 'get down, get down', and I saw this guy who appeared to have a bomb belt and wires coming out and people were panicking and I heard two shots being fired."