A man has been arrested after a van was driven into worshippers near a north London mosque.
Witnesses described seeing police giving emergency medical treatment to victims after the incident at 12.20am on Monday in Seven Sisters Road, Finsbury Park.
Many of the victims are believed to have just finished worshipping at the Finsbury Park mosque after breaking the Ramadan fast.
The Metropolitan Police described the attack as a "major incident" and said one person was in custody and there were "a number of casualties",
London Ambulance Service said: "We have sent a number of resources to an incident in Seven Sisters Road."
Pictures posted on social media show more than a dozen emergency vehicles at the scene.
Cynthia Vanzella said on Twitter: "Horrible to watch police officers doing cardiac massage at people on the floor, desperately trying to save them. I just hope they did."
A helicopter could be heard circling over Finsbury Park as police erected a large cordon in the area.
During Ramadan - the name of the ninth month in the Islamic calendar and the holiest time of their year - Muslims fast daily from dawn to dusk and focus on prayer, purification and acts of charity.
This year Ramadan began on May 26 and ends on Saturday June 24.
The Muslim Council of Britain confirmed that worshippers had been targeted in the attack.
A message on the council's Twitter feed read: "We have been informed that a van has run over worshippers as they left #FinsburyPark Mosque.
"Our prayers are with the victims."
Video posted online of the aftermath of the 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.
Witnesses at the scene said an elderly man who had collapsed at a bus stop was being tended to when the vehicle struck pedestrians.
A dozen police officers stood guard on a balmy Monday morning at the cordon at the junction of Yonge Park and Seven Sisters Road while several locals looked on.
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.
"It was around 11.30pm, 12-ish. I've been living here all my life. As a community, everyone's a family here.
"I initially thought it was my cousin.
Andrew, a courier who did not wish to give his surname, said he saw three people on the floor and at least one of them appeared to be in Muslim dress.
The 45-year-old, of St Albans, Hertfordshire, said he was driving back from a night shift when he saw the aftermath of the collision.
He said: "When I drove past slowly I could count three people on the floor and police were performing CPR on one of them.
"The guy having CPR performed on him was in a gown, ethnic clothing."
Jennifer Heape said: "Apparently a van has ploughed into people coming from #FinsburyPark mosque. People are reporting of several injured, some fatalities.
"Police are escorting people home very calmly. They are making sure people stay indoors.
"No panic, but it's very serious. A LOT of helicopters."
An eyewitness who lives on Seven Sisters Road told the BBC there were people "shouting and screaming".
She added: "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."
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. 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."