The bus was heading for Nagam in Kalikot district from Jumla district, carrying 29 passengers.
Thirteen people died on the spot, two others on their way to hospital and another two succumbed to their injuries upon reaching a hospital.
Three of the injured passengers are said to be in critical condition. One of the passengers escaped unhurt. A three- month-old boy also succumbed to injuries during treatment bringing the death toll to 18, Himalayan Times reported.
Others are being treated at Jumla-based Karnali Institute of Health Sciences. Meanwhile, police have identified all of the victims.
The incidents of road mishaps have increased in the recent past across the country which are attributed to poor road conditions, old vehicles and negligence of drivers.
On December 8 last year, at least 18 people were killed and 49 others injured when an overcrowded bus fell off a mountain road and rolled 600 meters down a slope in western Nepal.