"At around 16:20 (1520 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," police said in a statement as reported in the media.
No injuries were reported and police added that enquiries were ongoing.
Video footage from the incident showed a white car driving at low speed across Whitehall, where many government ministries are located.
The car then appeared to mount the pavement and came to a halt after hitting the large metal gates that guard the entrance to Downing Street.
Downing Street is a short walk from the Houses of Parliament, and the area has a high-security presence with barriers on pavements.