A bus carrying college students and their instructors back from a botany field trip drove off a highway in a mountainous area on Friday, leaving 21 dead and 15 injured, police said.
The bus plunged down a mountainous slope and rolled about 500 meters (1,640 feet), police said.
The Nepalese students and instructors from Krishna Sen Ichhuk Polytechnic Institute had been visiting a farm in a nearby district.
Rescue operations were difficult at the crash site near Ramri village, about 400 kilometers (250 miles) west of the capital Kathmandu, because the crash happened in a remote area and the wreckage was scattered.
The injured were taken to hospitals for treatment.
Vehicle crashes in in mountainous Nepal are generally blamed on poorly maintained vehicles and roads.
The accident happened a week after truck veered off a mountain road in Nepal, killing 16 people.