Eleven people have been injured after a vehicle mounted the pavement outside the Natural History Museum in west London.
Paramedics treated 11 people, primarily for leg and head injuries, and transported nine of them to the hospital, according to a statement from Peter McKenna, deputy director of operations for London Ambulance Service.
Workers in a cafe close the incident told how people fled the scene in a panic as police evacuated the area. Earlier, authorities had said a man was arrested, CNN reported.
The current terror threat level in the United Kingdom is "severe" - the second highest - meaning an attack is highly likely.
Labour leader Jeremy Corbyn tweeted: "Very concerning reports from outside the Natural History Museum".
"The incident is a road traffic investigation and not a terrorist-related incident", the statement said.More news: Kelly Bryant Suffers Apparent Ankle Injury vs. Wake Forest
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Meanwhile, government sources said Prime Minister Theresa May receives regular updates regarding the incident.
Panicky scenes ensued after the pedestrians were struck and it took almost four hours for police to reassure the anxious public that it was not another terrorist attack.
The incident occurred around 2 p.m.in an area popular with tourists because of a cluster of museums.
London's Metropolitan Police Service had said on Twitter than one man was detained in the South Kensington area of the city. A photo on Twitter showed three men holding down another man near a black vehicle.
"We were standing there for a moment, we didn't know what was going on and then the police came, more or less charging towards the crowd, and everybody was instructed to 'get out of there now!'"
A minicab driver sparked a major terror alert when his auto ploughed into pedestrians in the heart of one of London's busiest tourist areas, leaving 11 people injured.