At least 18 people died on the spot early Thursday when a bus fell off a highway and plunged into a river in western Nepal, the worst road accident in the country this year.

Ten passengers were seriously injured while a search is on for other passengers feared to have been trapped inside the bus, police said.

The accident occurred around 7 a.m. in a village called Kittu as the passenger bus run by the Kakre Vihar Yatayat, a private transport company, was heading towards Surkhet district from Dailekh.

It fell off the Kalikot-Surkhet highway into the swirling Karnali river below.

Overcrowding could have been the reason for the accident. The victims were yet to be identified, police said.