LONDON -- British emergency services raced to London's Natural History Museum after a car struck pedestrians Saturday outside the building. Police said the incident is not being treated as related to terrorism.

The London Ambulance Service says 11 people have been injured when a car crashed into pedestrians outside the Natural History Museum. One man was detained at the scene.

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.

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Police said later Saturday that the crash is being treated as "a road traffic collision."

London Mayor Sadiq Khan said he was in contact with police and emergency officials. He says "details are still emerging" about the incident.

Video captured on the scene showed a man on the ground being detained. It was not immediately clear if he was pinned down by police or others at the scene.

Police detain a man on the sidewalk after a car struck pedestrians near the London Natural History Museum. @RosaRodaNews / Twitter

Witness Katie Craine said she was coming out of the museum when she saw a man in handcuffs being pinned down on the ground by police near a damaged car.

"He looked really proud of himself," she told the Associated Press. "He was laughing."

The crash happened at 2:20 p.m. on a day when the central London museum is usually teeming with pedestrians, including international tourists.

A witness told BBC News that there were "tables knocked over at restaurants. People were screaming. And it was quite a scene at that stage."

"Panic rippled across the crowd. And it was busy, people were having to struggle to get out of there," the witness said.

BBC reporter Chloe Hayward said she was leaving the museum as the incident happened.

"I could see was 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.

Hayward added armed police were 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," she said.

The London Ambulance Service was tending to the injured. There was no immediate statement on the number or severity of the injuries.

Shopkeepers in the immediate area were told to evacuate and police established a large security cordon around the area minutes after the incident, closing some roads. Police helicopters circled the scene overhead.

Downing Street said British Prime Minister Theresa May was being briefed on the incident.

This is a developing story and will be updated.