Armed police immediately surrounded the silver auto 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. There is no ongoing chase.
A man has been arrested after a auto crashed into security barriers outside the Houses of Parliament and injured a number of pedestrians. There was no update provided on the people's conditions.
At least five police patrol cars attended the scene within minutes while armed officers were seen dragging the driver from the vehicle.
Police did not say if they suspected terrorism, calling it only a "collision".
Streets around Millbank, Parliament Square and Victoria Tower Gardens have been cordoned off.
"We're still trying to piece it together", a spokeswoman said.
Armed police immediately surrounded the silver auto 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.
Journalists in the area say the crash "looked intentional" and that the vehicle was driven into the security barrier "at speed".
She said: "I was walking on the other side of the road. I turned around and I saw a silver vehicle driving very fast close to the railings, maybe even on the pavement", she reportedly said. A series of ambulances arrived at the scene.
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.
BBC News Political Correspondent Jonathan Blake also tweeted that armed police at the scene told onlookers: "Move back as quick as you can, we're asking you for a reason".