A man has been arrested on suspicion of terrorism offences after a car crashed outside the Houses of Parliament, injuring several people.
Officers were seen surrounding the vehicle before the man in his late 20s was detained, shortly after 07:30 BST.
London Ambulance Service said it had taken two patients to hospital with non life-threatening injuries after cyclists and pedestrians were hit.
No one else was in the car and no weapons have been found so far.
"At this stage, we are treating this as a terrorist incident and the Met's Counter Terrorism Command is now leading the investigation," said Scotland Yard.
The man is in police custody at a south London police station and police are searching the vehicle, which is still at the scene.
A number of eyewitnesses have said the silver Ford Fiesta, which was travelling westbound, appeared to deliberately hit members of the public as it swerved into the opposite lane.
Footage released by the BBC shows the moment when the vehicle drives over a pedestrian crossing before crashing into the security barriers.