Police have confirmed they are investigating a terror attack in London after a van ploughed into people near a north London mosque, leaving one person dead and injuring eight others.

A 48-year-old man has been arrested on suspicion of attempted murder, and two of those hit by the van were said to be "very seriously injured”.

The prime minister, Theresa May, was woken to be told of the early morning incident at Finsbury Park and has confirmed that counter-terrorism command is leading an active inquiry. 

Deputy assistant commissioner Neil Basu, the senior national coordinator for counter-terrorism, said: "The attack unfolded whilst a man was receiving first aid from the public at the scene, sadly, he has died. Any causative link between his death and the attack will form part of our investigation. It is too early to state if his death was as a result of the attack.

"No matter what the motivation proves to be, and we are keeping an open mind, this is being treated as a terrorist attack and the counter-terrorism command is investigating.

"This was an attack on London and all Londoners and we should all stand together against extremists whatever their cause.”

Witnesses said the man who subsequently died had been taken ill and a small crowd had gathered around him to help. The van, they said, ploughed into those trying to assist him. 

The people struck were all Muslim, Basu said. Witnesses said some of them were wearing clothing that visually identified as such.

A witness said the driver had shouted "I want to kill all Muslims” before onlookers pinned him to the ground.

Police confirmed reports that members of the public had detained the driver, who was said to have gestured to onlookers after he was handed over to officers.

In an early morning statement, May said police were treating the van incident as a potential terrorist attack. She said: "I will chair an emergency meeting later this morning. All my thoughts are with the victims, their families and the emergency services on the scene.”

The mayor of London, Sadiq Khan, denounced the incident as "a horrific terrorist attack on innocent people in Finsbury Park. We don’t yet know the full details, but this was clearly a deliberate attack on innocent Londoners, many of whom were finishing prayers during the holy month of Ramadan.

"While this appears to be an attack on a particular community, like the terrible attacks in Manchester, Westminster and London Bridge it is also an assault on all our shared values of tolerance, freedom and respect.”

Cressida Dick, the Metropolitan police commissioner, said: "London is a city of many faiths and many nationalities. An attack on one community is an attack on all of us.

The attack took place outside the Muslim Welfare House, a few hundred metres away from Finsbury Park mosque. It was the third recent incident in London in which a vehicle has been used to kill, and Muslims who gathered in the area talked of fears of being targeted in hate attacks.