The night bus heading for Darchula from Dhangadi skidded some 200 meters down the road at Gwani village, some 700 km north west from Kathmandu, around 5:00 AM killing eight passengers on the spot.
The injured have been admitted to a local hospital. Nine of the injured are in critical condition.
Rescue work is being carried out with the help of police and local people shortly after the incident, police said.
The accident is likely to have caused by slippery roads as a result of continuous rains.