Police have said the incident in which a car mounted the pavement outside the Natural History Museum in London, sparking fears of a terror attack, was a traffic accident.
A man was dragged from the vehicle after it ploughed into pedestrians outside the museum on Saturday, injuring 11 people.
Moments later security guards, thought to be from the museum, appeared to drag the man from the black Toyota Prius - understood to be a licensed private hire vehicle - and bundle him to the ground.
The incident provoked a significant response from the police as dozens of armed officers flooded the area and a 200-metre cordon was created around the scene.
Witnesses fled in panic as police told them to "keep running" and put businesses around the area on lockdown.
One of those helping apprehend the suspected driver was Pixie Lott's fiancé Oliver Cheshire, who tweeted: "Thanks for messaging everybody. I’m ok. Thank you to the men who helped me pin him down and the police for coming so quickly."
Thanks for messaging everybody. I’m ok ❤ Thank you to the men who helped me pin him down and the police for coming so quickly.— Oliver Cheshire (@Oliver_Cheshire) October 7, 2017
He had been sitting in his silver Jaguar when the car struck his vehicle and claims the taxi was carrying three female passengers at the time.
"He looked at me and I was really in shock. I got out and grabbed him - three of us grabbed him - and someone phoned the police," he told MailOnline.
A passer-by, named as Maxim, added: "They took the man from the car and put him on the ground and then 20 minutes later evacuated the street. There was a lot of police, I saw people running people were panicking."
Within minutes of the incident armed police had arrived at the scene amid fears of a terrorist attack and Downing Street said Theresa May was “being kept fully informed” of developments.
Whitehall sources later said the incident was "not thought" to be a terrorist attack.
Nine people were left in need of hospital treatment following the collision.
Scotland Yard said in a statement: "Police were called at 14:21 on Saturday, 7 October to reports of a collision in Exhibition Road, South Kensington.
"It is believed that a number of pedestrians have been injured. Officers are on scene, and the London Ambulance Service have been called.
"A man has been arrested at the scene. Enquiries to establish the circumstances and motive are underway. If you have any information about this incident, please call 101."
One eye-witness suggested the driver may have lost control of his vehicle before it spun across the road and hit another car, then struck pedestrians.
Greg King, a banker at Goldman Sachs, told MailOnline: "A black Toyota went ploughing straight towards us and the crowd. At that point I thought it had lost control. It went spinning round and as it did that it smashed into a sign and knocked it over.
"In the meantime it hit at least two or three people. It then went careering across the road and smashed into the side of another car that brought it to a stop. People jumped out of the back of the car and everyone was running.
"A member of the museum staff and a member of the public dragged him on the ground."
The incident follows a number of attacks in which vehicles have been used to target pedestrians.
In March this year Khalid Masood drove a car into pedestrians on Westminster Bridge, killing four people and injuring more than 50 people before he was shot dead by an armed officer outside the Houses of Parliament.
The following month Islamist terrorists killed eight people and injured another 48 after using a van to drive into crowds on London Bridge before jumping out and stabbing customers in Borough Market's bars and restaurants.
Speaking moments after the incident outside the Natural History Museum, Emmanuel Hook, who was in the area at the time, said: "I was in a Chinese restaurant and all of a sudden all the diners just hit the floor and there were all these people running on Exhibition Road towards the station.
"It was really worrying seeing all these people panicking. All of a sudden a large gathering of police turned up in yellow vests, everyone was leaving their bags behind.
"People were panicking and running, no one knew what was going on, there were policemen saying 'go, go run'. We had to leave the restaurant and run off. I was worried there might be crazy people in the area trying to hurt people."
Another witness told Sky News: "I was getting off the Tube going to the Natural History Museum. The doors opened and 50 people came running down the escalator, it was mass panic.
"There was an announcement over the tannoy asking everyone to leave the Tube station. My family and I jumped back on the Tube as we thought the safest thing was to go to the next station.
"I saw a lady who had large bandages on her legs, she was in a wheelchair in an ambulance."
The incident came two weeks after a bungled attempt to blow a bomb up on a District Line train at Parsons Green station, in south west London.
A number of people suffered minor injuries after the device partially exploded on the train, sending commuters fleeing in terror.
An 18-year-old man was charged with attempted murder and causing an explosion likely to endanger life or cause serious injury after being arrested near the Port of Dover the following day.
He is due to appear at the Old Bailey on 13 October.
'Not thought to be terror'
Whitehall sources said the incident was "not thought" to be a terrorist attack.
London Mayor Sadiq Khan had earlier said: "Details are still emerging and I have spoken with and am in close contact with Assistant Met Commissioner Mark Rowley [head of UK counter-terrorism policing] and our other emergency services."
Police 'taking the lead' in investigation
Ben Farmer, the Telegraph's defence correspondent, reports that intelligence sources say police are taking the lead into the investigation, pouring over all the available evidence to establish what, if any, motive there was.
Church steps in to help
Members of Holy Trinity Church Brompton have been offering pastoral care to people at the scene.
A spokesman said none of their members were affected but they have attended the scene to offer help.
The Telegraph's Nicola Harley reports from the scene of the incident:
The police have formed a 300 metre cordon around the scene. The cordon, which is manned by armed police, stretches to the V&A Museum.
Museum staff have shut their doors to visitors as the incident unfolds and are only allowing tourists to leave the attraction. Dozens of people are lining the cordon to see what has happened, but those affected are still within the perimeter. At least 10 ambulances can be seen lining the street.
Man held after car strikes passers-by
A photograph posted on Twitter showed security guards holding down a man after pulling him from a car which hit several people.
Driver was pulled from car
An eyewitness called Maxim told Sky News: "They took a man on the ground, they took the man from the car and put him on the ground and then 20 minutes later evacuated the street.
"There was a lot of police, I saw people running people were panicking."
The nearby Science Museum was evacuated following the incident.
Theresa May 'informed'
Downing Street said the Prime Minister "is being kept fully informed" about the unfolding incident.
Eye witnesses tell of horror
Gabi Carter tweeted: "Just witnessed a car drive into people in London. Safe for now please message your friends if they are near the natural history museum."
Lesley Carter said: "Recommend steering clear of the natural history museum - police incident - man has mounted the curb in a car attempting to run people over."