Shortly after midnight, the hired vehicle swerved into a group of people leaving prayers at the Finsbury Park Mosque, one of the biggest in the country, witnesses said.
The 48-year-old driver of the van was detained by members of the public and then arrested by police on suspicion of attempted murder. No other suspects have been identified as part of the investigation, police said.
British Prime Minister Theresa May condemned the incident as an act of terrorism and an attack on Muslims.
"It was an attack that once again targeted the ordinary and innocent going about their daily lives. This time British Muslims as they left a mosque," said May who later visited the mosque.
Location: Finsbury Park Mosque, London
Neil Basu, a senior counter terrorism coordinator, told reporters it was too early to say what the motive of the attacker might have been, but that the incident was being treated as a terrorist 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 as a result of this attack."
Mr Basu said eight victims were being treated in hospital and two were in a very serious conditions. All were Muslim.
Muslim leaders said worshippers were specifically targeted after leaving prayers and linked the incident to a recent rise in anti-Muslim hate crime.
Witness Abdiqadir Warra told AFP the van "drove at people" and some of the victims were carried for several metres along the road.
London Mayor Sadiq Khan said it was a "horrific terrorist attack," calling it "deliberate" and aimed at "innocent Londoners, many of whom were finishing prayers during the holy month of Ramadan".
May said police had confirmed it was being treated as a potential terrorist attack and said she would chair an emergency response meeting later on Monday.
"All my thoughts are with the victims, their families and the emergency services on the scene," she said.
London mosque attacker: 'I want to kill all Muslims'
Worshippers leaving a London mosque just after midnight on Monday were helping an unwell elderly man when a van deliberately targeted them, eyewitnesses said, driven by an attacker who shouted: "I want to kill all Muslims".
The van swerved towards the people outside the Finsbury Park Mosque in north London just as they began to assist the man, who had collapsed.
"He turned left into the alleyway, and he just drove at people," eyewitness Abdiqadir Warra told AFP.
"Some of them he took a few metres. A man was inside in the van, I saw with my eye, and the old man was also on the ground, and I see some people were also injured. Some of them were very bad."
Locals then pounced on the driver and pinned him down while waiting for the police to arrive.
"The man, he tried to escape... but they caught the driver," Warra said.
Eyewitness Khalid Amin told BBC television that the van turned deliberately left and "just hit the people".
One man was trapped under the van and people tried to lift up the vehicle to free him.
Amin said that when people seized the driver, "he was shouting: 'All Muslims, I want to kill all Muslims.' Literally, he said that. Word by word."
Police said that one man had been arrested at the scene and that no further suspects had been identified.
Van collides with pedestrians near a north London mosque
'It's a terrorist attack'
Another eyewitness, who gave his name as Athman, told AFP: "People were screaming: 'It's a terrorist attack, it's an attack, this guy attacked us', and I had to run back and tried to save people who were still alive and giving water, helping the police.
"While he was in the police van he was waving for victory, he was very happy.
"He chose the time and he chose the place and he chose his target. So, it's the holy month of Ramadan.
"The time, he was planning for it, the target, he was planning for it, and the place -- outside a mosque."
Mohammed Kozbar, chairman of the Finsbury Park Mosque, called for Prime Minister Theresa May's government to take action.
The incident came after two terror attacks in London in the past three months involving vehicles ploughing into crowds of people, as well as the suicide bombing attack at a Manchester pop concert in May.
"People now have a big question about safety in London after all these terrorist attacks, and we want to assure them that they are safe, and that's why we want to work with the police," Kozbar said.
"People feel unsafe because after the terrorist attacks of London, Manchester, the increase of Islamophobia and hate crimes," he added. "This is very worrying to the Muslim community."
Several bunches of flowers had been deposited outside the mosque as commuters went to work on Monday morning.
Recent London attacks
It comes after two deadly Islamist attacks this year that used vehicles to ram pedestrians -- one earlier this month in the London Bridge area and a March attack in which a man drove a car into crowds on Westminster Bridge.
One witness, Abdul Rahman, told the BBC he saw the van "deliberately run over about 10 or 15 people". Rahman said he and another man wrestled the suspect to the ground and held him down for 20 to 30 minutes before police arrived.
A police statement said "One man was pronounced dead at the scene... Eight people injured were taken to three separate hospitals."
Two other people were treated at the scene for light injuries. Police said the male driver had also been taken to hospital as a precaution and would receive a mental health assessment.
Amateur video footage seen by AFP showed at least three people lying on the ground, including one who was receiving mouth-to-mouth resuscitation.
"Due to the nature of this incident, extra policing resources have been deployed in order to reassure communities, especially those observing Ramadan," the police statement said.
Bystanders rush to help victims near mosque at Finsbury Park
Prayers on the pavement
The Muslim Council of Britain (MCB), an umbrella body for British Muslims, said the incident occurred outside the Muslim Welfare House on Seven Sisters Road, near the Finsbury Park mosque.
"Over the past weeks and months, Muslims have endured many incidents of Islamophobia and this is the most violent manifestation to date," MCB head Harun Khan said.
AFP reporters saw a helicopter hovering overhead and several emergency vehicles blocking a section of Seven Sisters Road, a busy thoroughfare.
Police, including armed officers, could be seen manning a wide cordon around the area. Others searched the area with sniffer dogs.
A group of Muslim men were praying on the pavement nearby. Traffic was shut down along a one-kilometre section of the road.
Finsbury Park mosque was once a notorious hub for radical Islamists but has entirely changed in recent years under new management.
Its former imam Abu Hamza was jailed for life in New York on terrorism charges in 2015.
He preached there from 1997 to 2003 before being jailed for inciting violence. He was later extradited to the United States.
In 2015, the mosque was one of around 20 that took part in an open day organised by the MCB to promote better understanding of Islam following Islamist-inspired terrorist attacks in Paris.
Despite the change in leadership and a new focus on inter-faith relations, the mosque reported it had received a string of threatening emails and letters in the wake of the terror attacks in Paris.
Spike in anti-Muslim crime
Monday's incident in London follows an Islamist-inspired attack on June 3 in which three militants wearing fake suicide vests ran over pedestrians and went on a stabbing spree in bars in the London Bridge area.
They killed eight people before being shot dead by police.
London Mayor Khan said following that attack that there had been a 40-percent increase in racist incidents in the city and a fivefold increase in the number of anti-Muslim incidents.
On his Facebook page, Khan at the time called on Londoners "to pull together, and send a clear message around the world that our city will never be divided by these hideous individuals who seek to harm us and destroy our way of life".
Britain has seen two other attacks this year.
On March 22, a man drove a rented car into pedestrians on Westminster Bridge in London and stabbed a police officer guarding the British parliament to death before being shot dead.
Five people were killed in the attack.
On May 22, a suicide bomber blew himself up outside a pop concert in Manchester, killing 22 people.
— London Ambulance (@Ldn_Ambulance) June 18, 2017
— Metropolitan Police (@metpoliceuk) June 19, 2017