One detained after van strikes worshippers near London mosque, killing man in apparent terror attack

London police say one suspect has been detained in an apparent early-morning terrorist attack on worshippers standing outside a mosque.

Police say incident outside the Finsbury Park mosque in North London has all the "hallmarks of a terrorist incident".

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Police said a suspect was quickly and calmly turned over to the police, and that no one else was found in the van.

One man was killed and eight people were seriously injured.

Fabian Ali and Mohammed Mohidn, who witnessed the attack outside a London mosque, say one of the men looked "cracked off his face". Source: 1 NEWS

Police said the 48-year-old man who was driving the van was arrested and taken to a hospital as a precaution. He will be given a mental health evaluation.

The crash occurred at a time when the multiethnic neighbourhood was crowded with Muslims leaving the Finsbury Park mosque after Ramadan prayers.

Police said the driver was detained by the crowd until police arrived.

The crash occurred shortly after midnight when police received reports of a collision between a van and pedestrians. 

The Muslim Council tweeted that worshippers had been struck and said its prayers were with the victims.

London police closed the area to normal traffic. A helicopter circled above the area as a large cordon was established to keep motorists and pedestrians away.

Eyewitness told Sky News and other British media that the van seemed to have veered and hit people intentionally.

Mohammed Shafiq of the Ramadhan Foundation, a Muslim organisation, said that based on eyewitness reports it seems to be a "deliberate attack against innocent Muslims".

The Finsbury Park mosque was associated with extremist ideology for several years after the 9/11 attacks in the United States but was shut down and reorganised. It has not been associated with radical views for more than a decade.

Prime Minister Theresa May said police are treating the van incident "as a potential terrorist attack".

Norris helped the victims after a van with three men drove into a crowd outside a mosque. Source: 1 NEWS

"I will chair an emergency meeting later this morning. All my thoughts are with the victims, their families and the emergency services on the scene," Mrs May added.

Britain's terrorist alert has been set at "severe" meaning an attack is highly likely.

Earlier this month, a van veered into pedestrians on London Bridge, setting off vehicle and knife attacks that killed eight people and wounded many others on the bridge and in the nearby Borough Market area. Three Muslim extremists who carried out the attack were killed by police.

Manchester was also hit by a severe attack when a bomber killed more than 20 people at an Ariana Grande concert.