One man has been confirmed dead after a van was driven into a crowd of worshippers near a London mosque, in what police are treating as a terrorist attack and the British Prime Minister has described as an "attack on Muslims".

Key points: A van was driven into a crowd outside the Muslim Welfare House in Finsbury Park

A van was driven into a crowd outside the Muslim Welfare House in Finsbury Park One person was killed and 10 others injured, while the attacker was arrested at the scene

One person was killed and 10 others injured, while the attacker was arrested at the scene The man who died was receiving first aid prior to the attack, it is unclear if his death was caused by the attack

A white van was driven into the crowd near the Finsbury Park Mosque in North London just after midnight, as worshippers were leaving following Ramadan prayers.

The 47-year-old driver of the van was detained by members of the public and arrested by police.

The Metropolitan Police's counter-terrorism command is leading the investigation.

Counter-terrorism coordinator Neil Basu said the attack had "all the hallmarks of a terrorism incident".

Sorry, this video has expired Police hold back crowds in Finsbury park (Photo: AP)

UK Prime Minister Theresa May condemned the attack, describing it as a "sickening" attempt to destroy liberties that unite Britain, such as freedom of worship.

"This was an attack on Muslims, near their place of worship," she said outside Downing Street.

"Like all terrorism, in whatever form, it shares the same fundamental goal — it seeks to drive us apart and break the precious bonds of solidarity and citizenship that we share in this country."

A van is seen at Finsbury Park in north London after a vehicle struck pedestrians. ( AP: Victoria Jones )

Mr Basu said all victims were members of the Muslim community but that it was too early to determine the motive of the attack.

"The attack unfolded as a man was already receiving first aid at the scene, sadly that man has died," Mr Basu said.

"Any causative link between his death and the attack will form part of the investigation — it is too early to say if his death was a result of this attack.

The London Ambulance Service said eight people were being treated for injuries in hospital, with two others earlier treated at the scene for minor injuries.

But police appeared to discount earlier reports that some victims had been stabbed, saying none of the injured suffered knife wounds.

Ms May said extra police resources would be deployed to provide reassurance, and said Britain had been far too tolerant of all forms of extremism in the past.

Witnesses describe moment 'a big white van swerved in'

Footage posted on social media showed people lying on the pavement being given CPR, and a man with dark curly hair being led away by police.

Sorry, this video has expired Angry onlookers surround suspect being loaded into police van

"I saw at least two people being attended to on the ground. Shortly after police cordoned the area," said BBC producer Abdirahim Saeed, who was tweeting from the scene.

"People here say the attacker probably thought the place was a mosque and people just leaving late Ramadan prayers."

"It appears that a white man in a van intentionally ploughed into a group of worshippers who were already tending to someone who had been taken ill," assistant secretary of the Muslim Council, Miqaad Versi, said.

An eyewitness told the ABC that worshippers were "minding our own business, drinking tea, relaxing after the mosque" when "a big white van swerved in".

He said people in the crowd put the driver under citizen's arrest.

Sorry, this video has expired Driver detained after van hits worshippers

"The guy was smiling, he was happy," he said.

'An assault on freedom': London Mayor

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The Muslim Council of Britain said the incident was a "violent manifestation of Islamophobia" and called for increased security at Britain's mosques in the wake of the incident.

"During the night, ordinary British citizens were set upon while they were going about their lives, completing their night worship," secretary general of the Council, Harun Khan, said in a statement.

"It appears from eyewitness accounts that the perpetrator was motivated by Islamophobia."

London Mayor Sadiq Khan called the incident a "horrific terrorist attack on innocent people".

"It was an assault on our shared values of tolerance, freedom and respect," he said in a statement.

Mr Khan announced extra police would be deployed to reassure communities, especially those observing Ramadan.

Local people observed prayers on the street for the victims of the incident in the hours following. ( AP: Yui Mok, PA )

The leader of Britain's opposition Labour Party, Jeremy Corbyn, said in a statement on Twitter he was "totally shocked" by the incident.

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The Finsbury Park Mosque was associated with extremist ideology for several years after the 9/11 attacks in the United States but was shut down and reorganised. It has not been associated with radical views for more than a decade.

Earlier this month, a van veered into pedestrians on London Bridge, setting off vehicle and knife attacks that killed eight people and wounded many others on the bridge and in the nearby Borough Market area.

The three terrorists who carried out that attack were killed by police.

Witnesses described seeing the white van swerve into a gathering of people. ( Reuters: Neil Hall )

Map Interactive map showing Finsbury Park in northern London.

ABC/wires