A man has been arrested by armed officers on suspicion of criminal damage and dangerous driving, the police has said.
The silver Kia car crashed into the gates at around 4.20pm on Thursday and no one has been hurt, the Metropolitan Police said in a statement.
Downing Street video of Whitehall after car crash
Images on social media showed the car surrounded by emergency vehicles.
A Metropolitan Police statement said: “At approximately 16:20hrs on Thursday, 25 May a car collided with the gate of Downing Street on Whitehall.
“Armed officers arrested a man at the scene on suspicion of criminal damage and dangerous driving. He has been taken into custody.
“There were no reports of any injuries.
“Enquiries are ongoing to establish the circumstances.”
It is understood that Rishi Sunak was in Downing Street at the time the car crashed into the front gates.
The Prime Minister, who had been due to leave No 10 anyway, departed after the crash.
Speaking to PA News Agency, Witness Simon Parry, 44, said: “I heard a bang and looked up and saw loads of police with taser guns shouting at the man.
Nearly two hours after the crash, the Metropolitan Police released an additional statement, saying “A small cordon remains in place outside Downing Street after a car collided with the gates earlier this afternoon.
“The incident is being dealt with by local officers in Westminster and isn’t currently being treated as terror-related.”
“A lot of police vehicles came very quickly and were very quick to evacuate the area.”
Parry also said that the driver had his “face to the floor” as he was being arrested.
He said the man appeared to slow down before he reached the gates of Downing Street, having driven out from the other side of the road.
“There were sniffer dogs and a bomb squad.”
Asked to describe the mood in the immediate aftermath, Mr Parry said: “We saw people that were in a panic running away and we saw people who were excited.”