"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.
No injuries were reported and police added that enquiries were ongoing.
Prime Minister Rishi Sunak was reported by British media to have been in the building when the incident occurred, and left soon after.
Video footage of the incident showed a silver car driving at low speed across Whitehall, where many government ministries are located, having emerged from a pull-in area in front of the Ministry of Defense car park, opposite Downing Street.
It appeared to then mount the footpath and came to a halt after hitting the large metal gates that guard the entrance to Downing Street.
Other footage showed a police cordon surrounding the car, which appeared to be a Kia, with its boot open.
Simon Parry, 44, said: "I heard a bang and looked up and saw loads of police with taser guns shouting at the man.
"A lot of police vehicles came very quickly and were very quick to evacuate the area."
He added: "There were sniffer dogs and a bomb squad."
Dean Parker, 36, told AFP the driver "didn't look distressed. He looked like he must have had some sort of episode or something".
Parker, part of a protest on the opposite side of the street, said the car was not driving fast.
"It doesn't look like he tried to ram the gates off... It was a pretty slow impact. The police dealt with it pretty professionally and promptly."
Downing Street is a short walk from the Houses of Parliament, and the area has a high security presence with barriers on the footpath and in front of government buildings following previous incidents.
A man drove a car into pedestrians on the pavement close to parliament in 2017, killing four people.
He then crashed the car into the fence surrounding parliament and ran into the grounds, where he fatally stabbed a police officer. He was shot dead by an armed police officer.
Large gates were put up at the entrance to Downing Street in 1989 as a result of IRA bomb attacks in London, and the group launched three homemade mortar shells at the prime minister's residence in 1991.
The gates are the first line of security, with armed police stationed at the entrance. Official cars entering the street normally have to be checked before strengthened bollards are lowered to allow them through.
© 2023 AFP