One man died but police said it was unclear whether his death happened as a result of the attack.
The Metropolitan Police said eight people had been taken to hospital after the collision at the junction of Whadcoat Street and Seven Sisters Road, Finsbury Park.
A further two people were treated at the scene, where police arrested a man who had been held by members of the public amid angry scenes.
According to a witness who asked to be called Abdulrahman, which is not his real name, the driver of the van said: “I want to kill Muslims.”
Another witness, Adil Rana, 24, said: “The van was driving towards us to try and basically hit us at speed.
“When he got arrested, he was taunting, saying, ‘I’d do it again, I’d do it again’.”
Pictures of the van indicated it was rented from a company in South Wales, Pontyclun Van Hire.
The Metropolitan Police’s Deputy Assistant Commissioner, Neil Basu, said: “This is being treated as a terrorist attack and the Counter Terrorism Command is investigating.
“From 00:21hrs this morning police received a number calls to Seven Sisters Road.
“Officers were in the immediate vicinity as the attack unfolded and responded instantly. Additional officers arrived within 10 minutes.”
DAC Basu added: “I would like to thank those people who helped police in detaining the man and worked with officers to calmly and quickly get him into our custody.
“Their restraint in the circumstances was commendable.”
The 48-year-old man suspected of being the van driver was arrested on suspicion of attempted murder.
He was taken to hospital as a precaution and will undergo a mental health assessment.
Outside the police cordon, Communities Secretary Sajid Javid comforted a woman who was visibly shaking.
Mr Javid said: “I want to reassure both the local Muslim community, but also Muslims across the United Kingdom, that they will always have the full support of this government in fighting anti-Muslim hate crime.
“But I also want to learn today what further measures there are that can be taken by either the government, by police, by others to give them maximum reassurance.”
London Mayor Sadiq Khan said: “All of these are attacks on our shared values of freedom, of tolerance and of respect… and terrorism is terrorism, whether someone’s inspired by an Islamist narrative or other forms of ‘inspiration’.”
Theresa May is chairing an emergency Cobra meeting this morning, and is expected to give a statement in Downing Street afterwards.
“All my thoughts are with the victims, their families and the emergency services on the scene,” the Prime Minister said earlier.
The incident happened in Jeremy Corbyn’s constituency. The Labour leader said: “The response by all three emergency services was very timely and very quick. The gentleman who died’s body was on the ground and covered respectfully by a tent so that forensic examination could take place.”
The London Ambulance Service said it was called to the incident at 12.15am on Monday morning.
“We sent over 60 medics to the scene, including ambulance crews, advance paramedics and specialist responses teams and an advance trauma team from London’s Air Ambulance,” said the service’s Deputy Director of Operations, Kevin Bate.
It happened outside Finsbury Park’s Muslim Welfare House, which is not far from the Finsbury Park Mosque.
Toufik Kacimi, chief executive of the Muslim Welfare House, said the man who was arrested had to be rescued by the imam at the centre to stop him being attacked.
Mr Kacimi said when he did so, the driver said to him: “I’ve done my bit.”
The Finsbury Park Mosque said in a statement on its website: “This is a callous terrorist attack, which coincides with the murdered MP, Jo Cox, anniversary.”
The Muslim Council of Britain’s (MCB) general secretary Harun Khan said: “It appears from eyewitness accounts that the perpetrator was motivated by Islamophobia.
“Over the past weeks and months, Muslims have endured many incidents of Islamophobia and this is the most violent manifestation to date.
“Given we are approaching the end of the month of Ramadan and the celebration of Eid with many Muslims going to local mosques, we expect the authorities to increase security outside mosques as a matter of urgency.”
Asked about mosque security, Home Secretary Amber Rudd told Sky News: “We have a places of worship fund, which we announced last summer.
“We have made available two-and-a-half million pounds. I recently announced who would be getting those additional funds, which included 12 mosques, and actually I have repoened it recently to make sure that any additional place of worship that feels the need can apply for extra security.”
The Archbishop of Canterbury, the Most Reverend Justin Welby said: “The freedom to worship without fear is a
right we cherish as a nation and was won at great human cost over many years.
“The appalling attack on Muslims in Finsbury Park is an attack on us all and on the culture and values of our country.”
A delivery driver who was on a bike about three cars behind the incident, Mohammad Abdullah, told Sky News he saw the van take a sudden left turn.
“I think he done it on purpose. I was on a ped. He was about three cars in front of me. He came in a bus lane and took a sharp left.
“He went on top of the people. He actually ran them over. It was a white van.
“There was three of them. Two of them ran away. The other was held at the scene until the police came. Some people wanted to beat him up.
Mr Abdullah added: “I’ve seen about six or seven people on the floor. Most of them was male. It was exactly the same time as the prayers finished. As soon as it finished, this guy came. I think (the road he took) is a blocked road – It’s not even a through road.
“The other two got away. They must be somewhere around Finsbury Park. They ran away somewhere.”
“He had a tattoo on his back. He was not ill. He was not drunk. He got arrested by five or six police officers. They took him away. They never dropped him or nothing.”
He said in his opinion it was a terrorist attack.
Sky News reporters on the scene said it was tense – with one man shouting at police officers.
He claimed it took them one hour to arrive at the scene while “someone bled to death”.
Many at the scene expressed anger that the incident was not reported as a suspected terror attack sooner.
Another witness, Adil, told Sky News that the response time by police and the other emergency services was much longer than that taken after the London Bridge and Manchester attacks but other witnesses told Sky that the police response was very fast.
Transport for London said Seven Sisters Road had been closed northbound between Hornsey Road and Rock Street.