"Police were called just after 0020 hours (2320 GMT) 18 June to reports of a vehicle in collision with pedestrians," police said in a statement.
"There are a number of casualties being worked on at the scene. There has been one person arrested," the statement said.
The Muslim Council of Britain (MCB), an umbrella body, said on Twitter: "We have been informed that a van has run over worshippers as they left #FinsburyPark Mosque. Our prayers are with the victims.
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.
The mosque is near Seven Sisters Road, where the accident happened, and was once a notorious hub for radical Islamists but has entirely changed under new management.