Thirty-four Australians are among hundreds of tourists missing in Nepal after a thundering wall of water smashed through villages and caused catastrophic flooding.

At least 150 people were killed and 340 tourists remain missing after the disaster unfolded along the on the Himalayan border between Nepal and Tibet.

It’s believed a landslide of mud and rock upstream collapsed, triggering a huge wall of water that destroyed buildings and swept away houses, roads and power poles.

Verified ‌videos show the horrifying unfolding disaster, with dozens of people swept away, collapsed homes, floating cars and a metal bridge being washed away.

Witnesses told Reuters the waters engulfed entire villages.

Nepali officials said 403 people, including 341 foreigners, were reported missing.

Around 133 were from India on pilgrimage to Mount Kailash in Tibet, a sacred site for Hindus, said Sunil Sharma, a tourism board spokesman.

Also missing were 47 from the United States, 34 from Australia, 33 from the United Kingdom and 24 from Canada, he said.

Initial reports suggested an earthquake in the area could have triggered an avalanche and caused the floods, Nepali Foreign Minister Shisir Khanal told the country’s parliament on Wednesday, local media reported.

But it was later reported that seismic energy was generated by a landslide, according to the US Geological Survey.

From its origins in Tibet, the ​Bhote Koshi river empties into Nepal’s Trishuli river, which eventually flows into India as the Gandak river.

Security footage captured on the Chinese side of the Nepal-Tibet border showed many people fleeing before a torrent of rock, mud and water destroyed buildings, vehicles and took many lives.

With the deluge of muddy water sweeping down from an estimated nearly 2000 metres above sea level, flood alerts were issued in the populous northern Indian states of Uttar Pradesh and Bihar, which border Nepal and where several rivers flow down the mountains into the plains.

Authorities in Bihar said they had relocated about 5000 people from ‌six districts and planned to ‌move a total of 10,000 to 12,000 ⁠people.

At least 62 missing Nepali citizens were among hundreds of locals trekking in the Gosaikunda Lake area in Rasuwa, coinciding with the local festival of Janai Purnima on Friday.

Nepal police spokesman Abi Narayan Kafle told yhe Associated Press at least 28 police officials were missing.

Local media reported 65 people were being treated in hospitals in the area and in the capital Kathmandu.

South Korea separately said that eight of its citizens working on a hydropower plant were missing.

The exact cause of the mudslide could not be immediately determined but the German Research Centre for Geosciences said there was a 4.4 magnitude quake approximately seven minutes before the time shown on the security footage time-stamp.

An initial study of Planet Labs satellite imagery indicated that a landslide of snow and rock triggered a debris-laden flood in the Lhende river, about 20km northeast of the Nepal-China Rasuwagadhi border crossing, Nepal’s National Disaster Risk Reduction and Management Authority said ⁠on X.

Before and after images from Planet Labs appeared to show a wide swathe of destruction on either side of the usual ‌river course.

Qianggong Zhang, head of climate ​and environmental risks at the Kathmandu-based International Centre for Integrated Mountain Development, said the cause of the ice-rock avalanche into the Lhende Khola river on the Nepali side was yet to be confirmed.

“With a blockage still lodged upstream on the Nepal-China border ​river, authorities warn a ‌second flood may occur,” Zhang said.

Rescue helicopters could not land in Nepal’s affected areas of Syapru Besi and Timure in the mountainous district of Rasuwa, with a population of about 50,000, officials said, with the river flowing above its normal ​course.

-with AAP/AP