One man has died and eight people have been taken to hospital after a van was driven into pedestrians near a north London mosque.
The van driver, described by eyewitnesses as a large white man, was detained by members of the public after the attack in Seven Sisters Road at 12.20am on Monday.
One witness described being surrounded by bodies in the wake of the attack outside the Muslim Welfare House, close to Finsbury Park mosque.
Another said the attacker shouted about killing Muslims as he was held by local people.
The Metropolitan Police said in a statement: " One man was pronounced dead at the scene.
"Officers are in the process of informing next of kin. A post mortem examination will be scheduled due course.
"Eight people injured were taken to three separate hospitals; two people were treated at the scene for minor injuries."
Commenting on reports that the van driver also produced a knife, the statement went on: "At this stage there are no reports of any persons having suffered any knife injuries.
"The driver of the van - a man aged 48 - was found detained by members of public at the scene and then arrested by police in connection with the incident.
"He has been taken to hospital as a precaution and will be taken into custody once discharged.
"He will also be subject of a mental health assessment in due course."
The force said the investigation of the incident is being carried out by the Counter Terrorism Command.
Some witnesses at the scene said more than one attacker may have been involved.
But the Met said: "At this early stage of this investigation, no other suspects at the scene have been identified or reported to police, however the investigation continues."
The force added: " Due to the nature of this incident extra policing resources have been deployed in order to reassure communities, especially those observing Ramadan."
Prime Minister Theresa May said: "Police have confirmed this is being treated as a potential terrorist attack.
"I will chair an emergency meeting later this morning.
"All my thoughts are with the victims, their families and the emer gency services on the scene."
The attacker struck as the area was busy with worshippers who had been attending Ramadan night prayers at the mosque.
One resident told the Press Association he jumped out of the way as the van struck pedestrians.
The man, who did not want to be named, said: "The gentleman went straight down this road, people were just conversing, talking, just doing what we're doing.
"And he just came into all of us. There was a lot of people.
"I was shocked, shocked, shocked. There were bodies around me.
"Thank God I just moved to the side, I just jumped. Everyone is hurt. Everyone is actually hurt."
Abdulrahman Saleh Alamoudi said he was among a group of people helping an elderly worshipper who had fallen down when the van swerved towards them.
He told BuzzFeed: "I think at least eight or 10 people got injured. Luckily I managed to escape. And then the guy came out of his van and I got him.
"He was screaming, he was saying, 'I'm going to kill all Muslims, I'm going to kill all Muslims'. He was throwing punches.
"Then we managed to get him on the floor. Then he was saying, 'Kill me, kill me'. I said, 'We are not going to kill you. Why did you do that?' He wouldn't say anything."
But another witness at the scene said the attacker did not say anything.
Aweys Skeikh Ali said: "No, no, he was shocked."
The Muslim Council of Britain confirmed that worshippers had been targeted in the attack.
Secretary general Harun Khan said: "During the night, ordinary British citizens were set upon while they were going about their lives, completing their night worship.
"My prayers are with the victims and their families. It appears from eyewitness accounts that the perpetrator was motivated by Islamophobia.
"Over the past weeks and months, Muslims have endured many incidents of Islamophobia, and this is the most violent manifestation to date.
"Given we are approaching the end of the month of Ramadan and the celebration of Eid with many Muslims going to local mosques, we expect the authorities to increase security outside mosques as a matter of urgency."
Mr Khan added: "Many will feel terrorised, no doubt be angry and saddened by what has taken place tonight.
"We urge calm as the investigation establishes the full facts, and in these last days of Ramadan, pray for those affected and for justice."
There has been an increase in hate crime reports since the Manchester Arena bombing and the London Bridge attack.
Video posted online of the aftermath of Monday's attack showed a scene of chaos as people tried to help the injured.
One man could been seen giving CPR to a victim in the street while another man's head injury was treated with a makeshift dressing.
People could be heard shouting and screaming amid the chaos and bloodstains were visible on the pavement.
In one video, a group of men are seen holding the suspect to the ground as they call for the police.
Abdikadar Warfa said: "I saw a man underneath the van. He was bleeding. My friend said he had to lift the van.
"I was busy with a man who tried to escape. My friend said he said some words, but I didn't hear it.
"They (people who were hit) were mostly young. They are very bad.
"I tried to stop him (the suspect), some people were hitting him but I said stop him and keep him until the police came.
"He was trying to run away but people overpowered him. He was fighting to run away."
One man, who gave his name as Mohin, said his cousin was caught up in the incident.
The 32-year-old told the Press Association: "There were a lot of people in the street, crossing the street, going to mosque for prayers, for forgiveness, just to pray and go home and eat.
"They are doing their usual daily routine - they did not expect a van coming out of nowhere hitting them.
Images of the van showed it was rented from Pontyclun Van Hire in Pontyclun, near Cardiff.
Finsbury Park mosque was once infamous as the stamping ground of hook-handed hate preacher Abu Hamza.
But it was raided and shut down and later reclaimed by the local Muslim community, who have transformed it into a place which actively promotes better community relations across faiths.
In 2015 it was the target of an attempted arson when a white man with a jerrycan full of petrol tried to light it and throw it over the railings in front of the site before fleeing on a moped.