Authorities in Nepal used helicopters to search for survivors and drop emergency supplies to thousands cut off in towns and valleys after Wednesday's disaster swept a road thronged by trekkers and pilgrims that links Kathmandu with Lhasa in Tibet.
Police said they expected the death toll to rise beyond 270, with dozens of bodies swept down into the plains from where they were being recovered.
Nepali Home Minister Sudhan Gurung said the focus remained on finding survivors as rescue teams found 100 missing Indian visitors, mostly pilgrims, and 25 Chinese workers in the worst-hit region around Trishuli.
More than 650 foreigners were still unaccounted for while Nepali authorities were yet to determine the number of locals missing.
"It was a huge gush of mud coming straight towards us," said Keshav Prasad Baral, a 68-year-old survivor being treated in a Nepali 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."
The tally of missing in Tibet's Gyirong county was 558, Chinese state broadcaster CCTV said on Thursday, including 260 foreign nationals.
China said the death toll stayed at three.
The missing foreigners across both regions belonged to more than two-dozen countries, including 288 more from India, 63 from the United States, 51 from Malaysia, 35 from Australia, 33 from Britain and 25 from Canada.
China was in close communication with Nepal on search and rescue efforts, with almost 100 Chinese nationals in the affected area across the border in Nepal, the Chinese foreign ministry said.
China's Premier Li Qiang, the country's number two official, arrived at the disaster-stricken site in Gyirong on Thursday afternoon, state-run Xinhua news agency said.
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 in Nepal as the flows travelled downstream.
Ganesh Aryal, the administrator of Chitwan district, said authorities had recovered 103 bodies from the river system in his district which is about 100km away in the plains from the worst-hit region of Trishuli.
With local hospitals unable to accommodate all the bodies, district authorities were setting up tents and also making arrangements for families that were expected to arrive to claim their dead relatives, he said.
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 joined the rescue effort that retrieved 125 people on Thursday, including 20 foreigners, he said.
Nepali Prime Minister Balendra Shah left by road to assess the flood situation in one of the worst-affected districts of Nuwakot, his office said on social media.
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 complicate rescue efforts, particularly as rains are forecast, CCTV said.
Many of this week's victims were pilgrims headed to Kailash Mansarovar, a high-altitude site in Tibet revered by Hindus and Buddhists, among others.
Countries and organisations rushed or pledged help, with India, the United States, Canada and the United Nations saying they were providing assistance and closely monitoring the situation, with UN teams sending supplies and personnel to support affected communities.
