London Ambulance Service said it had sent "a number of resources".
Police said one person was arrested and that "a number of casualties [were] being worked on at the scene".
Vanzella said she went to the window and saw "loads of people gathering" in a corner across the road from her window.
One witness said that a van had hit about ten people returning from Finsbury Park mosque. Many police cars and ambulances were responding.
London's Metropolitan Police said officers were called just after midnight Sunday to an incident on Seven Sisters Road.
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Mohammed Kozbar, the chairman of the Finsbury Park Mosque, said in a Twitter post that "our thoughts and prayers with those who got injured and effected by this cowardly attack in Finsbury Park area" and said there were "many casualties in the floor".
London police have declared the crash a major incident and closed the area to normal traffic.
No other details were available immediately. Harun Khan, the head of the MCB, tweeted that the van had "intentionally" run over people leaving night prayers held during the holy month of Ramadan.
Earlier this month, three terrorists carried out a vehicular attack followed by a stabbing spree in London that left eight people dead and dozens wounded.