South African police say at least 14 children were killed when their school bus veered off the road and plunged into a lake near the southern city of Knysna on Wednesday.

Police say the bus driver was also killed in the accident. At least 40 other passengers were rescued and were treated for injuries.

Officials say most of the children on the bus were between the ages of seven and 17.

The cause of the crash is not immediately clear.