In the videos, a man can be seen retrieving a knife from the huddle on the ground before urging bystanders to get away.
George Robarts, a translator who was on the bridge at the time, said the unidentified man had run through traffic and jumped the central partition to tackle the attacker with several people.
“We ran away but looks like he disarmed him,” he said in a Tweet. “Amazing bravery.”
Rob Underwood, a 65-year-old from Lincolnshire, eastern England, who was visiting London for the day, said he heard bangs that sounded like a firecracker going off and did not initially realise they were gunshots.
“Once you see everybody rushing and scattering, you [are] really fearing for your own safety and I think the major thing was just to get out of the way and get down,” he told Reuters.
“You just feel very scared, very anxious about what’s happening and just wait for whatever is going to pass.”