The London Ambulance Service says 11 people were injured when a car crashed into pedestrians outside the Natural History Museum.
Deputy Director of Operations Peter McKenna said Saturday that nine of the injured were taken to the hospital for treatment, most with leg and head injuries.
Police said the incident was a road accident, not terrorism.
The crash happened at 2:20 p.m., London time, on a day when the central London museum is usually teeming with pedestrians, including international tourists.
Photographs showed a dented silver car and a man being pinned to the ground outside the museum.
Witness Katie Craine said she was coming out of the museum when she saw a man in handcuffs pinned down by police near a damaged car.
She said "he looked really proud of himself ... he was laughing.''
Shopkeepers in the immediate area were told to leave and police established a large security cordon around the area minutes after the incident, closing some roads.
Police helicopters circled the scene overhead.
The Natural History Museum tweeted that there had been a "serious incident'' outside the museum, which is located near the world famous Victoria and Albert Museum and other attractions.
Downing Street said British Prime Minister Theresa May was being briefed on the incident.