A long-haul passenger bus skidded off a bridge and tumbled into a river in northern Nigeria (search) on Sunday after the driver fell asleep, and 56 people were killed, officials said.

The luxury bus that began its overnight journey in the southern city of Lagos (search) careered off the Tamburaw Bridge (search) outside the northern city of Kano just before dawn, said Ibrahim Kano, a regional traffic official.

Six people were rescued from the wreckage, he told The Associated Press.

"From preliminary investigations it is obvious that the bus plunged into the river when the driver slept off as a result of fatigue associated with long night travel," he said.