Police said in a statement there were “a number of casualties”, adding that they were called to reports of “a vehicle in collision with pedestrians”at 0:20am (6:20am Thai time).
“We have been informed that a van has run over worshippers as they left #FinsburyPark Mosque. Our prayers are with the victims,” the Muslim Council of Britain (MCB), an umbrella body, said on Twitter.
Harun Khan, the head of the MCB, said the van had “intentionally” run over people leaving night prayers for the holy month of Ramadan.
An AFP reporter could see a helicopter and several emergency vehicles at the scene, which was closed off by a wide police cordon.
Traffic was shut down on a section of Seven Sisters Rd, where the incident happened.
“We saw lots of people shouting and lots of people injured,” David Robinson, 41, who arrived just after the accident, said.
MCB deputy head Miqdaad Versi said the incident happened “outside the Muslim Welfare House”, which is on Seven Sisters Rd near the mosque.
The London Ambulance Service said: “We have sent a number of ambulance crews, advance paramedics and specialist responses teams to the scene.
“Our priority is to assess the level and nature of injuries and ensure that those most in need are treated first and taken to hospital.”
Police described it as a “major incident”.
Finsbury Park mosque was once a notorious hub for radical Islamists but has entirely changed in recent years under new management.
Its former imam Abu Hamza was jailed for life in New York on terrorism charges in 2015.
He preached there from 1997 to 2003 before being jailed for inciting violence. He was later extradited to the United States.
In 2015, the mosque was one of around 20 that took part in an open day organised by the MCB to promote better understanding of Islam following Islamist-inspired terrorist attacks in Paris.
Despite the change in leadership and new focus on community relations, the mosque reported it had received a string of threatening emails and letters in the wake of the Paris attacks.
“If this attack is confirmed as a deliberate terrorist attack then this should be classed as an act of terrorism,” said Mohammed Shafiq, head of the Ramadhan Foundation community group.
“The British Muslim community requires all decent people to stand with us against this evil violence,” he said, adding that “rampant Islamophobia has been on the rise for a number of years”.
Today’s incident in London follows three Islamist attacks in Britain this year.
On March 22, a man drove a rented car into pedestrians on Westminster Bridge in London and stabbed a police officer guarding the British parliament to death before being shot dead.
Five people were killed in the attack.
On May 22, a suicide bomber blew himself up outside a pop concert in Manchester, killing 22 people.
And on June 3, three militants wearing fake suicide vests ran over pedestrians and went on a stabbing spree in bars in the London Bridge area.
They killed eight people before being shot dead by police.