British police arrested a man on suspicion of terrorism offences on Tuesday after he drove a car into security barriers outside parliament and injured at least two people.
London's Metropolitan Police said the incident, the latest apparent attack on Britain in the last 18 months, was being treated as a terrorism incident and its Counter Terrorism Command unit was in charge of the investigation.
Police said a silver Ford Fiesta had collided with a number of cyclists and pedestrians before crashing into barriers outside the Houses of Parliament at 0637 GMT.
"The driver of the car, a man in his late 20s, was arrested at the scene by armed officers," police said in a statement. "He was arrested on suspicion of terrorist offences. There was nobody else in the vehicle, which remains at the scene and is being searched. No weapons have been recovered at this stage."
London's Ambulance Service said it had treated two people at the scene and they had been taken to the hospital. Their injuries were not believed to be serious.
Armed police swarmed the scene and cordoned off a large area around the parliament in central London, usually bustling with tourists and government workers.
Witness Jason Williams said the car had struck a barrier on a lane used for access to the parliament building with force. He said he thought it was deliberate.
"It's a very serious incident," he told reporters. "There was smoke coming from the vehicle."
Images shot by a Euronews journalist showed police pointing their guns at a vehicle. Footage on social media showed a handcuffed man being led away by heavily armed police. Other footage showed a cyclist lying on the street.
"I saw the cyclists, injured cyclists. I've seen people, about 10, on the road, lying down, but I haven't seen any fatalities," Williams said.
British Prime Minister Theresa May (photo), who like other lawmakers is on holiday during parliament's summer recess, said her thoughts were with the people injured in the incident.
Westminster Underground station, close to parliament, was closed to the public and the building cordoned off.
In March 2017, Khalid Masood, 52, killed four people on nearby Westminster Bridge before he stabbed to death an unarmed police officer in the grounds of parliament. He was shot dead at the scene. It was the first of five attacks on Britain last year which police blamed on terrorism.
Britain is on its second highest threat level of "severe", meaning an attack by militants is considered highly likely and the authorities say a dozen Islamist plots had been foiled since Masood's attack.
Last week, a Muslim convert admitted plotting to kill more than 100 people by driving a truck into pedestrians on London's Oxford Street, the capital's major shopping thoroughfare.
In October last year, 11 people were injured when a car collided with pedestrians near London’s Natural History Museum, raising fears of an attack, but police later said the incident was a road traffic accident.
Meanwhile, the British government will hold a meeting of its Cobra emergency response committee to discuss the incident.