Thirty-three people were injured on Sunday, at least four seriously, when a Paris-London bus with passengers from nine countries overturned in northern France, police said.

The Flixbus vehicle toppled on its side around midday (1100 GMT) as it took an exit from the A1 motorway, France's busiest route, a police statement said. 

There were 33 people on board, of whom 29 sustained light injuries and four were seriously wounded, said the police, though the fire brigade put the number at five.

Of the injured, 13 were French and 20 foreign nationals - 11 from Britain, three from the United States, two from Spain, and one each from Australia, the Netherlands, Romania and Russia. 

They were taken to different hospitals in the region. 

Rescue teams from the police, fire brigade, and ambulance service rushed to the scene. The motorway exit has been closed, the statement said.

Flixbus said it was putting in place an emergency number and would provide a replacement bus.