BBC:- 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 appeared to deliberately hit members of the public.
BBC News home affairs correspondent June Kelly described the terror arrest as a “significant development”.
“The police will be looking at this man’s background, his identity – they’ll either know it or they will be working towards it,” she said. “They will be looking at his beliefs his associates, also his mental state.
“Also, crucially, is he on their radar – is he somebody who was known to them?”
Westminster tube station is closed and streets around Millbank, Parliament Square and Victoria Tower Gardens have been cordoned off.
People have been moved further back from the area twice as police put up a Terrorism Act cordon, officers at the scene said. Parliament is currently not sitting.
An eyewitness said the car was travelling westbound past the Houses of Parliament when it swerved into eastbound traffic.
Images posted to social media showed a man in handcuffs being led away from the car by officers after the crash.
Prime Minister Theresa May said: “My thoughts are with those injured in the incident in Westminster and my thanks to the emergency services for their immediate and courageous response.”
Home Secretary Sajid Javid also thanked emergency services for their quick response.