The bus en route to Kohalpur from Butwal in western Nepal, caught fire immediately after the accident at Khaskushma village of Banke district, according to the police.
Police said most of the passengers were carrying petroleum products with them as the country is reeling under acute fuel shortage due to the blockade on major trading points by the agitating Indian-origin Madhesi communities protesting against the promulgation of the new constitution.
The petrol filled jars and bottles ignited and fueled the fire, the police said.
Ten passengers were rescued alive from the burning inferno.
More From This Section
Most of the bodies of the deceased are burned beyond recognition, according to Superintendent of Police in Dang District Kuber Kadayat.
Passengers who escaped the ordeal said that the speeding bus went out of control, struck a tree nearly 25 meters off the road and immediately caught fire.
There were nearly three dozen passengers travelling on the bus.