By Michael Holden

LONDON, Oct 7 (Reuters) One man was detained after a number of pedestrians were injured in a collision with a car near the city's Natural History Museum on Saturday, and London police said they were trying to determine the circumstances. 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." Police described the incident as a collision. Unverified footage from the scene showed a man being pinned to the ground by four people. "Inquiries to establish the circumstances and motive are under way," police said. A spokeswoman for the London force said counter-terrorism officers were assessing the incident but had not yet reached a conclusion as to the circumstances. Earlier a spokesman told Reuters it was not being treated as a terrorism-related incident at this stage. Prime Minister Theresa May was being 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. A Reuters witness said there were large numbers of police, including armed officers, and paramedics at the scene although the atmosphere appeared calm. A BBC reporter at the scene said she could see a car diagonally across the road surrounded by a crowd of people with one or two on the ground. She said she was told by police injuries sustained were minor. A spokesman for the museum told Reuters that no one was being allowed into the building and people were being let out through a different exit. 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. REUTERS PS 2203