In the accident occurred at Damai Danda area of Kailali district in the wee hours, eight passengers died on the spot while four others succumbed while undergoing treatment in a local hospital, police said.
The bus was en route to Mahendranagar from Dipayal when it fell some 300 meters down the road.
According to a passenger, the accident occurred when the driver got off the bus to replace a deflated tyre in a downhill road without applying proper brakes.
The bus driver and his helper have been arrested.
Of the 29 passengers injured in the accident, five are in critical condition and have been taken to India for treatment, police said.
