HONG KONG — At least four people were killed and 11 more injured on Monday when an out-of-control school bus rolled down a Hong Kong street after the driver had exited the vehicle.

Video footage taken by another vehicle’s dashboard camera and spread widely across social media shows the driver leaving the bus after parking it along a sloped street in the North Point district. The bus immediately begins moving downhill, and the man runs in front of it to stop it.

The footage shows the bus rolling over the driver, dragging him about 20 yards, then grazing a taxi and appearing to pick up speed as it heads toward an intersection with King’s Road, one of the city’s main arteries.