At least 38 pilgrims were killed on Sunday when an overcrowded bus carrying them from India to a festival in southern Nepal swerved off a highway and plunged into a deep river.
The bus was taking the devotees -- 35 of whom were from the Indian state of Uttar Pradesh -- to a temple in Nawalparasi district, 150 km west of Kathmandu, police inspector Deepak Raya told AFP from the crash site.
"We have discovered 38 dead bodies. Five persons who jumped off from the bus before it plunged into the river are undergoing treatment at local hospitals," he said.
"Among them, there is one small girl, 10 women and the rest are men. We have not seen the bus -- it is still inside the water."
He said the survivors had told police there were around 75 people on board before the vehicle fell into the Gandak river, on Nepal's border with India. Three of the dead are Nepalis, he added.
"We are yet to find out the cause of the accident. The water level in the river was high as it is monsoon time so the bus on its way to Triveni sank... after skidding away from the road," Raya told AFP.
"Many of those who died are from Maharajganj district of Uttar Pradesh. They were here to attend the annual religious festival at Triveni and worship Lord Shiva on Monday morning."
More than 100 police officers and soldiers have been deployed to scour the Gandak and its banks for survivors.
July marks the beginning of the monsoon season in Nepal, when rivers which have become parched in the first half of the year begin to swell up again, posing a greater threat to vehicles which lose control.
A speeding bus plunged off a mountain road in western Nepal last month into a deep ravine, killing 10 people.
A bus crash on a remote stretch of mountain road in the east of the country that killed 41 people in October last year was described as the most deadly for several years.
The bus, carrying around 60 people, plunged 300 metres (1,000 feet) onto a river bank after losing control and swerving off a narrow section of highway.
Nepal's road network has seen a four-fold expansion over the last 25 years, but that has been accompanied by a rising death rate. Official figures showed 1,734 fatalities in 2010, up from 879 in 2001-2.