Several pedestrians have been injured after a car ramped over the pavement into a crowd of people near the Natural History Museum in London, police say.
Video footage that emerged on Twitter showed a man being restrained on the ground.
BBC reporter Chloe Hayward who was at the scene described the incident;
“I could see a car diagonally across the road, looking like it was going into one of the boulders on the side of the road, and I could see a crowd of people around what was clearly one or two people on the pavement,” she said.
She added there were now armed police at the scene.
“We have had lots of police coming onto the scene, helicopters above, and I can see an ambulance which is definitely having someone put in, but it isn’t clear how bad that injury is.”
London Metropolitan Police say one person had been detained following the incident at 14:20 BST in Exhibition Road in South Kensington and inquiries are under way to establish the circumstances and any motive. .
A Downing Street spokesman said the UK Prime Minister is “being kept up to date on events”.
The current terror threat level in the UK is “severe” – the second highest.