Witnesses spoke of people trampling over each other and hiding in toilets as the attack unfolded.
One witness, Olly Foster, said he heard people screaming "run, run, there's a guy literally stabbing everyone", and believed it might have been a Halloween related prank.
He recalled people surging through the carriage and that when he looked down at his own hand, it was "covered in blood" and there was "blood all over the chair" that he had been leaning on.
An older man "blocked" the attacker from stabbing a younger girl, leaving him with a gash on his head and neck, Olly said.
Another passenger, named Gavin, told Sky News that he saw a victim moving through his carriage saying: "They've got a knife, I've been stabbed."
"They were making their way through the carriage to get away from the suspects. They were extremely bloodied," he added.
He says by the time the train stopped, "they were basically on the floor".
"That person ended up collapsing on the floor. They were taken to an ambulance pretty much straight away," he said.
When it was finally safe to leave the train Gavin said he saw "The armed police were pointing to the suspect as we came off the train.
London Underground worker Dean McFarlane said that he saw multiple people running down the platform bleeding, with one man in a white shirt "completely covered in blood".
He said he grabbed people and told them to leave the station, and tried to assist passengers who he believed were having panic attacks.
Ten people have been taken to hospital, nine of whom have life-threatening injuries.
Two people have been arrested and counter-terrorism police have been called in to join the investigation.
