A car has rammed into the gates outside Downing Streets, according to local reports.
Whitehall has been closed by the police following the incident.
It is believed one person has been arrested.
Rishi Sunak was inside No 10 when it happened and the building was put into lockdown.
In a statement released on Twitter, the Metropolitan Police 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. Inquiries are ongoing.”
Pictures of the arrested man have since emerged.
Rishi Sunak has been evacuated from Number 10 out of the back entrance