A "number of pedestrians" were injured when a car crashed into barriers outside Britain's Houses of Parliament on Tuesday, with armed police swooping in to arrest the driver, Scotland Yard said.
"The male driver of the car was detained by officers at the scene," the police statement said. "A number of pedestrians have been injured."
None of the injuries are believed to be "life-threatening", said police, who were yet to say if they suspected terrorism.
London Ambulance said they had treated two people at the scene for non-serious injuries and taken them to hospital.
Armed police immediately surrounded the silver car after it crashed at 7.37am (06:37 GMT), pointing guns at the driver as he was removed from the vehicle, according to footage posted on Twitter.
Later images showed police holding the man, dressed in jeans and a black puffer jacket, in handcuffs as roads and Underground stations around parliament were sealed off.
Witness Ewalina Ochab told the Press Association that the incident "looked intentional".
"I was walking on the other side. I heard some noise and someone screamed," she said.
"I turned around and I saw a silver car driving very fast close to the railings, maybe even on the pavement.
"I think it looked intentional — the car drove at speed and towards the barriers."
Westminster was the scene of a terror attack last year, when Khalid Masood, a 52-year-old British convert to Islam, drove a car at pedestrians on a bridge over the River Thames, before fatally stabbing a policeman on guard outside parliament.
The attack left five people dead and around 50 injured, and only ended when police shot Masood dead.
Britain endured a tumultuous period following the March 22 rampage, with four further terror attacks, including three in the capital at London Bridge, Finsbury Park and Parsons Green tube station.