The toll from a bus crash in western Nepal has risen to 47, making it one of the country's deadliest road accidents in years, police said on Monday, as rescuers searched for more bodies.

Emergency workers pulled the bodies of 44 victims from the wreckage of the overcrowded bus over the weekend after it plunged into a deep river in mountainous Jajarkot district on Thursday.

The bodies of three other victims had earlier been found, and police said rescuers were still searching for more victims in the deep, fast-flowing river.

Deadly crashes are relatively common in the impoverished Himalayan nation because of poor roads, badly maintained vehicles and reckless driving.

"The confirmed death toll so far is 47," said Jajarkot police chief Dinesh Raj Mainali.

"We have recovered all the bodies that were trapped inside the bus wreckage. Now we are searching for any bodies that may be outside the bus."

Police believe the accident happened when the bus driver saw a tractor approaching from the opposite direction and swerved to avoid it, sending the vehicle off the narrow road, Mainali said.

There were only 45 people on the official passenger list, but police believe the driver stopped along the route to pick up extra travellers without registering them.

"There are 42 seats inside the bus so it was somewhat overloaded," Mainali said.

Ten injured passengers were taken to a nearby hospital for treatment after the bus plunged into the river.

Distraught families packed the hospital Monday morning, anxious for news of their loved ones.

The country's road network has seen a four-fold expansion over the last three decades, but that has been accompanied by a rising death toll.

According to official figures, 1,816 people lost their lives in accidents in a one-year period between 2012-13, up from 682 deaths ten years ago.

A total of 41 people died in October 2011, when a bus carrying around 60 passengers en route to Kathmandu plunged onto a riverbank.

A Russian woman was among 10 people who died this month when two buses collided along a national highway in central Nepal.

Last month a crowded bus plunged down a hill in a town outside Kathmandu, killing 14 people including two Israelis.