Eleven people have been injured and a man detained by police after a car ploughed into pedestrians in one of London's busiest tourist areas, sparking a terror alert.

Video footage posted on Twitter showed a man being restrained on the ground by members of the public after the incident near the Natural History Museum (NHM) in South Kensington on Saturday afternoon.

The incident sparked fears of a terrorist attack in an area busy with families, but Scotland Yard later confirmed it was being treated as a road traffic collision and was "not being treated as a terror-related incident".

The 11 people treated were mostly suffering from head or leg injuries, the London Ambulance Service said, with nine taken to hospital.

A Metropolitan Police spokesman said: "Whilst inquiries continue it is believed a car mounted the pavement and collided with a number of pedestrians.

"Eleven people were found at the scene with varying injuries and nine of them have been taken to hospital, and this includes the man that was detained by police.

"Their injuries are not believed to be life-threatening or life-changing.

"The man detained by officers is currently under arrest and is in custody at a north London police station.

"The incident is a road traffic investigation and not a terrorist-related incident."

Downing Street had said that Prime Minister Theresa May was being kept up to date with developments.

Pictures and footage from the scene showed street damage and a massive police presence in the capital's museum district, home to the NHM, the Science Museum and the Victoria and Albert Museum.

Eyewitnesses spoke of pedestrians fleeing in terror as the drama unfolded shortly after 2.20pm.

Dieon Rurora, 25, who works in a nearby cafe, said: "People were running down the street, falling over. It was quite scary."

Colleague Merilin Mueller, 20, added: "It just seemed like an accident because there was a police car. We couldn't see outside.

"Then there were loads of police cars and that's when all of these police came marching down saying, 'move, move'.

"They said, 'you need to evacuate'."