Eleven people were injured on Saturday when a car collided with pedestrians near London's Natural History Museum, in one of the capital's busiest tourist areas, but police doused concerns it was a terrorist attack, saying it was a road traffic incident.

Police said it was believed the car had mounted the pavement outside the popular attraction in west London and collided with a number of pedestrians.

Officers had arrested a man aged in his 40s at the scene and he was now being questioned on suspicion of dangerous driving after being taken to hospital for treatment.

Britain has suffered five attacks blamed on terrorism so far this year, three of which involved vehicles, and the incident in an area packed with tourists at the weekend had prompted concerns that the collision had been a deliberate act.

"The incident is entirely a road traffic investigation and is not a terrorist-related incident," a police statement said.

London's ambulance service said they had treated 11 people, mostly for head and leg injuries, with nine taken to hospital. Police said none of the injuries were life-threatening or life-changing and the majority of those hospitalised had now been discharged.

Unverified footage from the scene showed a man being pinned to the ground near a crashed black Toyota car.

Oliver Cheshire, a model who is the fiancé of British pop singer Pixie Lott, told the Daily Mail newspaper he was one of those who had helped detain the man. He said three female passengers in the car told him it was a private-hire taxi.

"He was driving down the pavement and hit 11 to 12 people. Then the guy was screaming," he told the paper. "He looked at me and I was really in shock. I got out of my car and grabbed him — three of us grabbed him — and someone phoned the police."

Cheshire later wrote on Twitter: "Thanks for messaging everybody. I’m ok. Thank you to the men who helped me pin him down and the police for coming so quickly."

Neither police nor Transport for London, which runs most of the city's transport system, would comment on the status of the vehicle.

"My thanks to the first responders at this incident this afternoon and the actions of members of the public. My thoughts are with the injured," Prime Minister Theresa May said on Twitter.

Britain is on its second highest security alert level, meaning an attack by militants is considered highly likely.

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. The same month, a van was driven into worshippers near a mosque in north London which left one man dead.