Kathmandu  - At least six people were killed and more than 20 others injured when a passenger bus plunged off a mountain highway in central Nepal, police said Saturday.

Police said the driver lost control of the bus trying to avoid a truck coming from the opposite direction. It dropped into Trishuli River near the town of Mugling, about 90 kilometres west of Kathmandu Friday night.

"The bus fell about 100 metres off the highway and smashed into rocks on the river bank some 100 metres below," a Mugling police officer said. "Most of the victims died after they were crushed in the wreckage of the bus."

Nearly half of the 21 people injured in the accident were reported in serious condition. The bus was en route to the southern town of Narayanghat from Pokhara in western Nepal. (dpa)