Eleven people have been injured after a minicab driver ploughed into pedestrians near to the Natural History Museum.
The incident sparked a full-scale security lockdown in South Kensington, west London, when the vehicle mounted the pavement on Saturday afternoon.
Video footage posted on Twitter showed the driver being detained on the floor with damaged cars in the background.
There was a heavy armed police and emergency service presence immediately after.
Scotland Yard said later the incident was not being treated as terror related, and described the collision as a “road traffic collision”.
Victims are being treated for a range of head or leg injuries, London Ambulance Service said.
Tommy Gallagher, 37, had just been to the NHM with his six-year-old son when the incident happened.
He told ITV News: “It just went mad. People were screaming ‘run, run’. It was a stampede.
“Some poor woman and a child in a pram were trampled over. It was horrible.
“My little boy thought a monster was chasing us.”
Pictures and footage from the scene in Exhibition Road showed street damage and a massive police presence in the upmarket area, home to the NHM, the Science Museum and the Victoria and Albert Museum.
Some images showed the black Toyota Prius, registered with Transport for London (TfL) as a minicab, that had collided with a silver Vauxhall saloon and a Jaguar.
The area is a magnet for tourists, including lots of families with young children.
In a message on Twitter, the Prime Minister said: “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.”
A Metropolitan Police spokesman said: “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.”