London’s Metropolitan Police said the man was pronounced dead at the scene. Eight others were taken to three area hospitals and two were treated at the scene.
The driver of the van, aged 48, was detained by members of the public at the scene and then arrested by police in connection with the incident, authorities said.
He was taken to the hospital and will be subject to a mental health evaluation.
Counter-terrorism police were leading the investigation.
The Muslim Council said in a tweet that worshippers were struck by the van while leaving prayers near Finsbury Park mosque. It said its prayers are with the victims.
London police have declared the crash a major incident and closed the area to normal traffic. A helicopter circled above the area as a large cordon was established to keep motorists and pedestrians away.
Eyewitness told Sky News and other British media that the van seemed to have veered and hit people intentionally. Police did not confirm that.
Mohammed Shafiq of the Ramadhan Foundation, a Muslim organization, said that based on eyewitness reports it seems to be a “deliberate attack against innocent Muslims.”
The neighbourhood has two mosques, and several hundred worshippers would have been in the area after attending prayers as part of the Muslim holy month of Ramadan.
The Finsbury Park mosque was associated with extremist ideology for several years after the 9/11 attacks in the United States but was shut down and reorganized.
It has not been associated with radical views for more than a decade.
Prime Minister Theresa May described the crash as a “terrible incident.” The statement from her office said her thoughts were with the injured, their loved ones and emergency services who responded to the scene.
Jeremy Corbyn, leader of Britain’s Labour Party, said in a tweet he was shocked by the incident.