Twenty-three people died in western Nepal when a bus carrying school students and teachers back from a botanical field trip plunged into a gorge, police said.

The students were aged mostly between 16 and 20. Two teachers and the driver also died in the accident early evening on Friday in a remote area.

The vehicle was carrying 37 people, with 22 killed at the scene and another in a nearby hospital. Fourteen people were treated for injuries.

"Our preliminary investigation shows the cause of the incident was speed," police officer Bel Bahadur Pandey told AFP.

Road accidents are relatively common in Nepal because of poor roads, badly maintained vehicles and reckless driving.

The latest comes a week after a truck accident in central Nepal killed 20 mourners returning from a funeral ritual.