Details are emerging of the moments following a terror attack in London which has killed at least one person and injured scores of people.

There are claims the attacker, who allegedly mowed down scores of pedestrians outside a London mosque, taunted his victims as they lay injured or dying.

Bystanders at the scene of the have told news.com.au the man was icily calm, laughed and was even "blowing kisses" moments after he ran down at least 10 people.

Emerging from the white van that was used as a weapon, it's claimed the man said he had "done his bit".

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London's Metropolitan Police have now described the incident as a terrorist attack.

Hussain Ali told news.com.au he heard a bang and ran towards the site of the carnage in Finsbury Park, around 7 kms north of London's CBD.

"They were saying he was proud. He was waving his hand and laughing. [They] said he timed the attack to follow prayers.

"He chose to get as much casualties as possible, he came exactly at the time to get as much people as he wanted," Mr Ali said of the incident which happened just after midnight as worshippers were exiting two seperate mosques from prayers.

"It was panic, people were running for their lives."

A shop owner outside one of the suburb's two mosques, who did not want to be identified, told news.com.au, "He jumped out and ran towards the dead end."

He told news.com.au that he wouldn't repeat what the driver was saying, but, "We heard words that made people want to do bad stuff to him... it made people realise he did this on purpose.
"The thing that got me was that he was so calm. Even when he killed the guy he was laughing, blowing kisses."

"That's cold hearted".

Rabies Rafa, 42, said: "He just laughed. They just killed people and he laughed.

"He had just ran people over up the sidewalk and killed innocent people.

"It was horrible to witness."

Police said the pedestrian ramming, which occurred outside the Muslim Welfare Centre mosque on the busy Seven Sisters Road, was a suspected anti-Muslim terror attack outside a mosque in north London.

Police confirmed a man was pronounced dead at the scene and counter-terrorism forces are investigating. Eight injured people were taken to three separate hospitals and two were treated at the scene for minor injuries.

UK Prime Minister Theresa May called the attack "every bit as sickening" as the other terrorist attacks of the past month.

"We will come together to condemn this act and to say once again that hatred and evil of this kind will never succeed."