Rescuers in Nepal used helicopters to search for survivors and drop emergency supplies to thousands cut off after Wednesday's disaster swept a rugged mountainous region thronged by trekkers and pilgrims linking Lhasa in Tibet with the Nepalese capital of Kathmandu.
Police said they expected the death toll to rise beyond 165.
"This will go up, as we have resumed the search and more bodies are expected to be recovered," police spokesperson Abi Narayan Kafle told Reuters.
Almost 600 foreigners were among 826 people missing in Nepal, police and tourism officials said.
Among the missing tourists from more than two dozen countries, 177 were from India, 63 were from the United States, 34 from Australia, 33 from Britain and 25 from Canada.
The tally of missing in Tibet's Gyirong county was 558, Chinese state broadcaster CCTV said on Thursday, including 260 foreign nationals.
Verified videos showed crushing masses of water and debris sweeping away dozens of people at a border crossing in Gyirong, with homes, roads and power projects washed away further downstream in Nepal.
"It was a huge gush of mud coming straight towards us," said Keshav Prasad Baral, a 68-year-old survivor being treated in hospital.
"As it got closer, it kept rising higher and higher. When I saw it enter our home, I tried to grab my wife's hand and take her to the terrace. But she was swept away by the mud."
A helicopter ferried him to safety four hours later.
"My wife is still somewhere beneath the mud," he said. "She's gone."
In the hardest-hit districts, helicopters were dropping tents, food and other emergency supplies provided by neighbouring India, said Raja Ram Basnet, a spokesperson for Nepal's army.
More than 5000 army and police rescue personnel were mobilised to look for survivors and find bodies.
Early reports from Nepali officials suggested an earthquake in the area could have caused the lower part of a glacier to collapse and trigger the floods.
The US Geological Survey said an earthquake with magnitude initially reported as 4.4 was in fact seismic energy generated by the collapse of glacial rock and ice, followed by debris flow.
Chinese authorities have identified risks from a still-dammed lake in Gyirong, upstream from the mudslide and flood-stricken Tibet-Nepal border crossing that could significantly complicate rescue efforts in the mountainous site, CCTV reported on Thursday.
Many of the victims were making a pilgrimage to Kailash Mansarovar, a high-altitude site in Tibet revered by Hindus and Buddhists among others.
The US State Department said it was sending a disaster response adviser and providing assistance of $US500,000 ($A697,000).
Canada was also closely following the situation, Prime Minister Mark Carney said on X, describing the floods as "absolutely devastating".
UN teams and partners were sending supplies and personnel to support affected Nepali communities, Secretary-General Antonio Guterres said.
Security footage captured on the Chinese side of the border showed many people fleeing from a torrent of rock, mud and water that destroyed buildings and vehicles.
People seeking information about family members missing from the affected areas of Nuwakot and Dhading gathered outside a Nepali army training centre that was the base for helicopter rescue operations, the images showed.
An initial study of Planet Labs satellite imagery showed a landslide of ice and rock unleashed a flood carrying debris in the Lhende River, about 20km northeast of the Nepal-China Rasuwagadhi border crossing, Nepal disaster management officials said on X.
Television images showed collapsed homes, floating cars and a metal bridge being washed away, while witnesses said the waters engulfed entire villages.
"There is devastation everywhere we look," said Tula Bahadur BK, a health worker in Rasuwa.
"The settlements next to the river have been completely swept away. Five of my own relatives are missing."
