The bus heading towards Butawal from Arghakhachi district collided with the truck at Narpani area, situated 400 km west of Kathmandu killing 18 people.
The accident occurred yesterday on a turn where the road was barely wide enough for two large vehicles to pass, an eyewitness said.
The truck loaded with some 200 cooking gas cylinders overturned and hit the speedy bus.
The bus fell some 150 metres down the hilly road after it was hit, while the truck just overturned.
Also Read
Remaining people were undergoing treatment at Lumbini Zonal Hospital in Butwal.
The truck driver and three people inside it managed to save their lives by jumping from the vehicle.
The gas cylinders in the bus were scattered and hit the already injured passengers, the police said.
All those killed in the accident were the bus passengers.
In another incident, a jeep which arrived for rescue works overturned at the accident site and a man was killed and few others sustained injuries.