"Our priority is to assess the level and nature of the injuries and ensure those in the most need are treated first and taken to hospital".
A leader of the Muslim Council of Britain has called for extra security at mosques after a van struck worshippers leaving prayers at the Finsbury Park mosque.
Britain's terrorist alert level is now at "severe", meaning an attack in highly likely. "I've been in touch with the mosques, police and Islington council regarding the incident", Corbyn wrote.
The force said the investigation of the incident is being carried out by the Counter Terrorism Command. The crash occurred at a time when the multiethnic neighborhood was crowded with Muslims leaving the Finsbury Park mosque after Ramadan prayers.
One man, who gave his name as Mohin, said his cousin was caught up in the incident.
London police have arrested a man following reports of a vehicle smashing into pedestrians at Seven Sisters Road in north London around midnight local time.
The London Ambulance Service said it was responding to the incident.
Mohammed Kozbar, chairman of Finsbury Park mosque, told The Sun: "Whoever did this, he did it to hurt people and it's a terrorist attack".
He said: "When I drove past slowly I could count three people on the floor and police were performing CPR on one of them".More news: Cristiano Ronaldo in focus after Confederations Cup tie
The mosques were busy with people observing the holy month of Ramadan.
Some witnesses at the scene said more than one attacker may have been involved.
Mrs May added: "All my thoughts are with those who have been injured, their loved ones and the emergency services on the scene".
"We should make clear that if this attack is confirmed as a deliberate terrorist attack then this should be classed as an act of terrorism".
He added: "I said, 'tell me why did you try driving to kill innocent people?' Our prayers are with the victims".
Earlier this month, three knife-wielding Islamist attackers unleashed a terror rampage in the British capital, plowing a van into pedestrians on the London Bridge before stabbing revellers in a nearby market, killing seven people.
According to multiple reports and social media posts, the van ran over people leaving the Finsbury Park Mosque.
Witnesses said a van veered off the road into crowds outside Finsbury Park mosque, the Independent newspaper reported.
Transportation officials said roads in the area were being closed.
The Metropolitan Police described it as a major incident.