Experts warned of the risk of further floods a day after the devastating tsunami-like wall of freezing water and mud wiped out towns under a torrent of sludge, engulfing homes, smashing bridges and dams, and sweeping vehicles away like toys.

Many of the missing are foreign tourists, including trekkers in the Himalayan nation, as well as scores of Hindu pilgrims to Tibet's sacred snow-capped Mount Kailash.

The US Geological Survey (USGS) said the disaster was caused by a glacial collapse that triggered a vast flow of icy debris.

Climate change is causing glaciers to melt worldwide, increasing the risks of glacial lake floods and glacial collapses.

Emergency teams were racing to pluck survivors from affected zones, while Nepali soldiers used sniffer dogs to search for bodies buried under the suffocating dirt.

"It is a giant graveyard," Omkar Joshi, a 35-year-old Nepali customs agent rescued from a hilltop in the border town of Timure, told AFP. "All that is left are sand and pebbles, soaked red by human blood."

Nepali police said they had recovered 389 bodies.

Another 910 people, including 517 foreign tourists, were out of contact in the country. Beijing said 100 Chinese citizens -- not accounted for in that tally -- are also missing in Nepal.

Indians make up the largest number of missing foreigners, while the United States said 90 of its citizens were out of contact.

In China, state media said the "mudslide disaster" at the Gyirong Port in Tibet killed three people, while 558 people, including 260 foreigners, are missing.

Chinese Premier Li Qiang visited the area on Thursday, state media said, to oversee relief work.

China's Tibet Autonomous Region is largely inaccessible to foreign journalists.

Prime Minister Balendra Shah, who urged the nation to "stand together" hours after the disaster, toured some of the hardest-hit areas on Thursday.

Shah told local authorities to "provide immediate relief to displaced families" and to open blocked roads, his office said in a statement.

Other foreigners out of contact include citizens from Australia, Britain, Malaysia, the Netherlands, Portugal, South Africa and South Korea, Nepal's tourism board said.

The sudden rush of mud and debris was "like an inland tsunami", travelling nearly 170 kilometers south into Nepal, said environmental historian Ruth Gamble, of Australia's La Trobe University.

Buddhist spiritual leader the Dalai Lama, who lives in exile in India, said he would "pray for all those who have lost their lives".

Chinese government officials in Tibet mobilised nearly 800 emergency workers, as well as sniffer dogs and speed boats to help the rescue efforts, the official Xinhua news agency said.

Promises of aid and assistance began to trickle in soon after reports of the scale of the disaster.

The USGS said a glacial collapse caused seismic activity and had "catastrophic" downstream impacts in Nepal and Tibet.

"This event was initially reported as a magnitude 4.4 earthquake," it said, but the seismic recordings were analysed and it was found instead to be a "glacial collapse and debris flow".

Fears of more potential floods remain, with water trapped by the immense piles of debris blocking the valley.

"With a blockage still lodged upstream on the Nepal-China border river, authorities warn a second flood may occur," said Qianggong Zhang, head of climate and environmental risks at the Kathmandu-based International Centre for Integrated Mountain Development.

Kathmandu's Flood Forecasting Division issued a "special notice" on Thursday, warning of a growing lake behind debris left by the landslide and urging extreme caution.

Scores of Hindu devotees from across the world are among the hundreds missing on the border, Indian spiritual leader Sadhguru said on Thursday.

They were returning from a holy pilgrimage to Mount Kailash, on the Chinese side of the frontier, when they were caught in the floods at an immigration post.

"The entire group was there in the building," Sadhguru said in a video message to his millions of followers, weeping as he spoke from Tibet, with the anguished wails of other pilgrims heard in the background.

"This is a terrible and extraordinary event."

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