Eyewitness Abdul Rahman said the driver had said he wanted to "kill all Muslims" and told the BBC he struck the man and helped subdue him.
Metropolitan Police's deputy assistant commissioner Neil Basu said the "terrorist attack" began when the van was driven into a man who was already being given first aid by the public on the pavement.
Labour leader and Islington North MP Jeremy Corbyn said on Twitter : "I'm totally shocked at the incident at Finsbury Park tonight.
Mr Corbyn also said he would be attending prayers at Finsbury Park Mosque later on Monday with Islington Council Leader Richard Watts.
Image copyrightAFPImage copyrightEPALabour's shadow home secretary and Hackney North and Stoke Newington MP Diane Abbott said on Twitter that police "must urgently review security for all mosques".