Updated 7pm

Eleven people were injured after a car ploughed into people outside London's Natural History Museum earlier today.

British media reported a car had mounted the sidewalk outside the tourist attraction, one of several large museums in that area of South Kensington, west London, and police said a man had been detained at the scene.

"A vehicle has collided with pedestrians near the Natural History Museum entrance at Exhibition Road," the museum, one of the most popular visitor attractions in the country, said in a statement.

"We are working with emergency services to assess the incident and we are doing all we can."

Police said at 7pm that they were treating the incident as a "road traffic collision" and had ruled out terrorism, after hours of uncertainty about the circumstances surrounding it. Unverified footage from the scene showed a man being pinned to the ground by four people.

"Inquiries to establish the circumstances and motive are under way," police said.

Prime Minister Theresa May was being updated, a spokesman said, adding it was usual practice in such circumstances.

Earlier, London Mayor Sadiq Khan said he was in close contact with the police's most senior counter-terrorism officer.

London's ambulance service said they had treated 11 people, mostly for head and leg injuries, with nine taken to hospital.

Police at the scene. Photo: Reuters

Tourist magnet

The area is a magnet for tourists, including lots of children.

Afra Wang posted a picture of emergency services on Twitter, writing: "A crime scene? Full armed police locked the whole area out outside of @V_and_A in London. The helicopter above us doesn't seem to leave."

Video footage on Twitter showed a man being restrained on the ground in the middle of Exhibition Road.

None of the four people around him are in uniform.

Behind them is a black Toyota car with its driver's door open, which appears to have collided with a silver Vauxhall saloon.

Police at the scene. Photo: Reuters

The Natural History Museum tweeted: "There's been a serious incident outside the Museum. We are working w/ @metpoliceuk and will provide an update when we have more information."

Britain is on its second highest security alert level, meaning an attack by militants is considered highly likely, and there have been five attacks already this year, three involving a vehicle.

In March, a man drove a car into pedestrians on London's Westminster Bridge killing four before stabbing a police officer to death in the grounds of parliament.

Three Islamist militants drove into people on London Bridge in June before stabbing people at nearby restaurants and bars, killing eight and the same month a van was driven into worshippers near a mosque in north London which left one man dead

Police at the scene in South Kensington. Photo: Reuters