The suspected terrorist was wrestled to the ground by passers-by after he had careered, reportedly smiling, through a crowd of pedestrians, including a man in a wheelchair.
Eyewitness Hussain Ali, 28, said that, while being restrained, the man was protected by the people he is thought to have been targeting.
He said: "The leader of the mosque said 'You do not touch him'. He was sitting and holding him like that, people kept holding him.
"All the police and helicopters came after around eight minutes."
Mr Ali described the horrifying scene unfolding outside the Islamic centre in north London early on Monday morning.
"All I heard was a banging, then I turned and saw all the shouting and running.
"I saw people taking a man from underneath the van, he was black, bleeding, he was not dead, he was alive.
"There was a man in a wheelchair, a man underneath the van, it was hell.
"People who were inside saw the attacker was smiling, he was waving, he was happy.
"It was panic, people were shouting, screaming, some saying it was an accident.
"It was panic, it was horror."
In the wake of the carnage, the valour of an imam called Mohammed Mahmoud was also hailed by the religious community.
Toufik Kacimi, chief executive of the Muslim Welfare House, said his "bravery and courage helped calm the immediate situation after the incident and prevented further injuries and potential loss of life".