"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.
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.
"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.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)