VIDEO: UK PM Johnson's car hit in collision outside parliament

The car carrying British Prime Minister Boris Johnson was crashed into from behind in central London on Wednesday after taking evasive action when a pro-Kurdish demonstrator ran on to the road.

The protester was stopped and detained, according to a journalist on the scene, after he ran towards Johnson's Jaguar as it was leaving under police escort from the Houses of Parliament.

A video posted online showed the car braking before being struck by the following vehicle in the convoy, causing a large dent, while police wrestled the protester to the ground.

The protester was believed to have been demonstrating about Turkish action against Kurdish rebels.

Police detain a man after running in front of Boris Johnson's car in London. AP

The Metropolitan Police confirmed the collision, which happened at about 2:30 pm in Parliament Square.

"The police vehicles were part of a security movement," it said in a statement.

"A pedestrian is reported to have stepped onto the road, causing the vehicles to suddenly stop, which has led to two of the vehicles in the convoy being involved in a damage-only collision." No injuries were reported and a man was arrested at the scene on suspicion of a public order offence and obstructing the highway, the force added.

"All vehicles were able to drive from the scene," it said.

Agence France-Presse