One person has been arrested after a car hit the main gates of Downing Street.
Police said there were no injuries.
Pictures broadcast on television showed cordons in place along Whitehall.
“At around 4.20hrs a car collided with the gates of Downing Street on Whitehall,” Metropolitan Police said in a statement.
“Armed officers arrested a man at the scene on suspicion of criminal damage and dangerous driving.
“There are no reports of any injuries.”
Footage of the incident showed a small silver hatchback which appeared to come out of a car park next to the Ministry of Defence building.
The vehicle crosses Whitehall, near the Cenotaph, before abruptly breaking and then driving forward directly into the gates of Downing Street.