Metropolitan Police confirmed a man was arrested at the scene near Finsbury Park mosque on Seven Sisters Road.
One eyewitness told Buzzfeed News the attacker jumped out of the van with a knife, shouting "I'm going to kill all Muslims".
"We managed to get him to the floor and held him down, then he said: 'kill me, kill me'.
A police officer at the scene confirmed the incident was being treated as a terrorist attack.
"Police were called just after 0020hrs 18 June to reports of a vehicle in collision with pedestrians," the police said in a statement.
People at the scene told reporters they held the man on the ground for thirty minutes before the police arrived.
The van crashed into a group of Muslims as they were leaving Taraweeh prayers at Finsbury Park mosque.
An eyewitness told LBC radio the attack resembled "something from a horror movie, everyone running everywhere".
Another eyewitness reported that bystanders "confronted" the van driver and "held him down until police came".
The van used in the attack was connected to a hire company based in Mid Glamorgan, south Wales - a three hour drive from north London.