A man has died and ten people have been injured after a van ploughed into pedestrians near a north London mosque, BBC reports.
The van mounted the pavement and struck a group of people just after midnight near Finsbury Park Mosque in Seven Sisters Road. A 48-year-old man has been arrested.
British Prime Minister Theresa May said police were treating it "as a potential terrorist attack".
The Muslim Council of Britain said a van intentionally ran over worshippers.
Counter terrorism officers are at the scene, the Metropolitan Police said.
Many of the victims are believed to have just left evening prayers at the Muslim Welfare House after breaking the Ramadan fast.
The MCB said it was a "violent manifestation of Islamophobia" and called for extra security around mosques.
The UK PM will chair an emergency meeting later.
She described it as a "terrible incident", adding: "All my thoughts are with those who have been injured, their loved ones and the emergency services on the scene."
Extra police are being deployed to reassure communities, especially those observing Ramadan, Mayor of London Sadiq Khan said.
The van driver was arrested after being detained by members of the public at the scene following the collision at 00:20 BST.
Police said there were no reports of anyone suffering from knife injuries after speculation at the scene the driver was armed with a knife.
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.
Video posted online of the aftermath showed a scene of chaos as people tried to help the injured.
One man could be seen giving CPR to a victim in the street while another man's head injury was treated with a makeshift dressing.
An eyewitness told how he jumped out the way of the van as it struck.
He said: "He just came into all of us. There was a lot of people. We got told to move straight away.
"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."
Another who lives in a flat on Seven Sisters Road told the BBC she saw people "shouting and screaming".
"Everyone was shouting 'a van's hit people'.
"There was this white van stopped outside Finsbury Park Mosque that seems to have hit people who were coming out of the mosque after prayers finished."
She said the road was "backed up" with police cars, ambulance and fire engines.
Some witnesses at the scene - near Finsbury Park Station and the Emirates stadium - 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."
Labour leader and Islington North MP Jeremy Corbyn said on Twitter: "I'm totally shocked at the incident at Finsbury Park tonight.
"I've been in touch with the mosques, police and Islington council regarding the incident. My thoughts are with those and the community affected by this awful event."