Number 10 has been placed in lockdown after a car attempted to drive into Downing Street.
Armed officers arrested a man on suspicion of criminal damage and dangerous driving after a car collided with the gates, the Metropolitan Police said.
Staff in Downing Street were told they could not leave as police officers attempted to secure the scene.
Rishi Sunak, the Prime Minister, is understood to have been inside the Downing Street complex when the incident took place.
A Number 10 source said the driver of the car was a man. Details are still emerging about what exactly took place.
A Metropolitan Police spokesman said: “At around 16:20hrs 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.
“Enquiries are ongoing.”