The Seti burst its banks near the city of Pokhara, a popular tourist hub, on Saturday, sweeping away an entire village
Rescuers scouring Nepal's central Annapurna region after severe flash flooding said Sunday that there was almost no hope of finding survivors and that the final death toll could be more than 60.
The bodies of 17 people have been recovered but district police superintendent Sailesh Thapa told AFP that 47 missing people, including three Ukrainian tourists, were feared dead.
"So far, 12 of the 17 bodies have been identified. An excavator has reached the worst affected areas and is clearing the mud," he said.
"We have a list of another 47 people who have gone missing. Their chances of survival are almost zero. The three Ukrainians are still missing."
Just eight people have been rescued since the Seti burst its banks near the city of Pokhara, a popular tourist hub, on Saturday, sweeping away an entire village, and swamping families enjoying picnics on the river banks.
Most of the missing are thought to be local.
One witness, named as Uddha Bahadur Gurung, described how the river had suddenly swollen with water and turned into a lethal surge.
"There was nothing unusual. People were enjoying picnics, some were relaxing in the hot spring pools by the river and others working," he told the Kathmandu Post.
"Out of nowhere came this swelling dark murky water with debris, sweeping away many people."
Sniffer dogs have been sent 200 kilometres (125 miles) from the capital Kathmandu to search for bodies along the banks of the river, which has now subsided, while police and army personnel hunted for survivors.
Prime Minister Baburam Bhattarai broke off from key political negotiations over forming a new government to visit Kharapani village, which was washed away by the flood, his spokesman told AFP.
"He has instructed the authorities to bring 20 excavators so that the dead bodies of those who have been buried by the floods can be recovered," said Bishwadeep Pandey, personal secretary to the premier.
"The prime minister has also committed the government to provide expenses for the last rites to family members of those who died."
A landslide caused by days of heavy rain had blocked the Seti near its origin in the snow fields and glaciers of the Himalayas, said Nepalese Army spokesman Ramindra Chhetri.
"Then there was a powerful outburst, which resulted in a flash flood in the Seti river that entered human settlements and created havoc," he told AFP, adding some houses were covered with mud up to 12 feet (3.5 metres) deep.
"We have mobilised a company, an engineer platoon and soldiers from specialised troops for search and rescue operations," he said.
The 8,091-metres (26,545-feet) Mount Annapurna attracts thousands of trekkers, both local and foreign, each year as well as day-trippers who enjoy picnics on the banks of the Seti river.
The mountain is considered both technically difficult and avalanche-prone and has a much higher death rate among climbers than Everest, the world's highest peak.