London police said a incident outside the city's Natural History Museum in which 11 people were hurt when a car collided with pedestrians was not terrorism-related but was being treated as a road traffic collision.
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."
Prime Minister Theresa May was updated, a spokesman said, adding it was usual practice in such circumstances.
London Mayor Sadiq Khan said he was in close contact with the police's most senior counter-terrorism officer.
Britain is on its second highest security alert level, meaning an attack by militants is considered highly likely. There have been five attacks described by the authorities as terrorism this year, three involving vehicles.
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.
The Natural History Museum is the fourth most popular tourist attraction in the United Kingdom, with 4.6 million visits during 2016, according to the Association of Leading Visitor Attractions.