British police have sealed off the road outside Finsbury Park tube station in north-east London, after reports a van has driven into people in the area.
Witnesses saw the van swerved to hit pedestrians near a mosque.
A man was shown on video being held by police behind a police vehicle. British police have confirmed one man has been arrested.
A man was shown on video being held by police behind a police vehicle. British police have confirmed one man has been arrested and taken into custody.
British media outlets are reporting witness accounts that at least one person was stabbed in the incident, which unfolded just after midnight London time.
Sky News London said a number of casualties were being treated at the scene and the Metropolitan Police said it was dealing with a "major incident".
London Ambulance Service tweeted that a number of paramedics were attending to victims on the busy Seven Sisters Road which is one of the main thoroughfares in the area north of the Thames.
Witnesses reported seeing a white hire van veer off the road and into a group of pedestrians standing near a mosque just after midnight.
We have sent a number of resources to an incident in Seven Sisters Road. More information will follow when we have it.— London Ambulance (@Ldn_Ambulance) June 18, 2017
Screams were heard as the van ploughed into the crowd who were understood to have just finished a prayer meeting.
"Horrible to watch police officers doing cardiac massage at people on the floor, desperately trying to save them. I just hope they did," witness Cynthia Vanzella tweeted.
Ms Vanzella lives in a flat overlooking the road, describing the scene as "really, really ugly".
She told Sky News people often congregate outside the mosque following prayer meetings but gatherings were generally very quiet.
She said she was about to go to sleep when she heard shouting outside and went to her window to look at the chaotic scene unfolding.
The London Telegraph reported bystanders wrestled the van driver to the ground and pinned him down until police arrived.
London Ambulance Service deputy director of operations Kevin Bate released a statement saying the most seriously injured people were the first to be taken to hospital.
The Australian government's travel advisory service Smart Traveller has warned Australians to avoid the area, which remains sealed off and under police guard.