A van packed with migrants has swerved off a road in southern Serbia, injuring 40 people, some of them seriously.

Serbian police say the accident happened early Tuesday and the driver fled the scene. It was not immediately clear what caused the van to slide off the road.

Doctors at an emergency hospital in the area say five people remain in a life-threatening condition with spinal, head or abdominal injuries. They say the migrants came from the Middle East and Africa.

Serbia and the rest of the Balkans have become a transit route for the smuggling of migrants seeking to reach western Europe.