"At around 16:20hrs [local time, 15:20 GMT] a car collided with the gates of Downing Street on Whitehall. Armed officers arrested a man at the scene on suspicion of criminal damage and dangerous driving. There are no reports of any injuries," the police said in a tweet.
Video of the incident showed the vehicle momentarily accelerate before approaching the gate at what appears to be a rolling stop pace.
Media reports have indicated that UK Prime Minister was in his office when the gate was struck, and that he had later been spotted leaving in a motorcade.
The police said the incident was not "being treated as terror-related," adding that a small cordon was in place outside Downing Street and local officers in Westminster were dealing with the incident.
An investigation into the incident remains ongoing.