The ill-fated bus was heading towards Rasuwa district, 150 kms north of Kathmandu and home to the popular Langtang trekking route, when the driver lost control and the vehicle fell some 150 metres down the hilly road in Ramche village, they said.
Those killed include an infant and 12 women, police said.
About 30 passengers, who were injured in the accident have been admitted to the hospital.
There were also reports of about 70 persons on board the bus when the incident occurred.
Nepal Army personnel, police and local people were involved in rescue operation after the crash.