A bus packed with people returning from a village fair drove off a mountain highway in Nepal on Thursday, killing 16 people and injuring 20 others.

The bus rolled about 300 meters (984 feet) down a mountain slope before it slammed near a river in west Nepal, government administrator Karunakar Awasthi said.

Rescuers were struggling because of darkness and remoteness of the area but managed to recover the bodies and take the injured to hospitals.

Awasthi said the bus appeared to have dragged on the road before veering off, indicating there could be a brake failure. The road was wide enough for three buses to easily pass and there was not much traffic on the route, he said.

The cause of the crash wasn't immediately clear but accidents are mostly blamed on poorly maintained vehicles and roads in mountainous Nepal.