SEVERAL people are injured and a taxi driver has been detained after a car rammed into crowds outside London's Natural History Museum.
The incident happened around 2.20pm London time (12:20am AEDT) in Exhibition Rd, South Kensington.
A senior government security source reportedly said the driver of the car blacked out, Tim Shipman, The Sunday Times political editor said on Twitter.
The man pictured being restrained on the ground is understood to be the driver of the smashed-up Toyota.
The Metropolitan Police have just confirmed the incident was not a terror attack, but an accident.
"The incident at Exhibition Road is not being treated as terror-related,'' they tweeted, almost four hours after the incident. "It is a road traffic collision.''
The London Ambulance Service said they treated 11 people, including nine who were taken to hospital.
Most had received head and leg injuries.
Hundreds of terrified tourists fled the scene as the black Toyota Prius - a registered minicab - careered into a sign before ultimately crashing into a crowd of as many as 10 people as it hit a silver car.
Witnesses said a blood-soaked man was pinned to the ground and was "laughing" as he was detained.
Roxanne Dervliet, from Bristol, was yards away when she saw police bundle on top of a man on the ground.
She told Sun Online: "We'd just walked past the museum and saw what looked like a car crashed into a building.
"There were 100-odd people running away.
"Police were directing people out of the way and I think one person started running and it set everyone off.
"I was shaking, my friend was crying.
"My first thought was that it was terror-related.
"My mum was calling me and telling me I shouldn't have come to London for my birthday.
"I went into Starbucks opposite to get out of the way.
"Everyone is very confused about what is going on. We're all shook up."
One American tourist, who did not wished to be named, was with his girlfriend in the KFC restaurant just yards from the smash.
He told Sun Online: "We were sitting down and suddenly saw a huge stampede of people. Some police came in and told us to get on the floor.
"Then they told us to get in the basement.
"They were pushing everyone forward and telling them to run."
The Metropolitan Police said a number of pedestrians had been injured in a "collision''.
"Officers are on scene and the London Ambulance Service have been called,'' the Met tweeted.
"A man…has been detained at the scene.
"Enquiries to establish the circumstances and motive are underway.''
The Natural History Museum, a few blocks away from Hyde Park, is popular with locals and tourists alike and the area was busy with pedestrians braving a chilly autumn day in London.
The museum is one of London's most popular attractions and brought in more than 4.6 million visitors in 2016.
Nearby museums including the Science Museum and Victoria and Albert Museum were evacuated with Tube stations sealed off by police.
Twitter users said the car had mounted the footpath and rammed into the crowds, resulting in several people being injured.
Nearby Cromwell Road, a major thoroughfare, was shut down by police, causing heavy traffic congestion in parts of central London.
The Natural History Museum tweeted there had been a "serious incident outside the Museum.''
"We are working with (the Met police) and will provide an update when we have more information.''
Downing Street said British Prime Minister Theresa May was being briefed on the incident.
London's official terrorist threat level has been set at "severe," indicating an attack is highly likely.
London has seen three fatal terror attacks this year where a vehicle was used to mow people down - at Westminster Bridge, London Bridge and outside a mosque in Finsbury Park.
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