A glacial collapse triggered the catastrophic flash flood in Nepal and Tibet that roared down valleys, wiping out entire villages and leaving a preliminary death toll of at least 165 people, the US Geological Survey said. Rescuers on Thursday raced to locate the hundreds missing, including nationals from India, the US, UK, Australia and Canada.

Terrifying videos from the event on Wednesday showed a massive wall of water crashing down on the border as people attempted to flee. Trucks were upended and houses, roads ⁠and power projects swept away in Nepal, while ​officials in Tibet said they feared “major casualties” after a mudslide hit a border land crossing.

In the affected areas, houses, trees and vehicles were submerged or buried in mudslides. Helicopters hovered overhead all day in the area bringing in survivors.

Nepal’s tourism ministry said 468 tourists and travellers, including 393 foreign nationals, were unaccounted for in the mountainous ⁠region popular with trekkers and pilgrims. Chinese state media said at least 558 were missing on the Tibet side of the border, of whom at least 260 were foreign nationals.

The missing foreigners included 142 Indian nationals, 47 people from the US, 34 from Australia, 33 from Britain and 24 from Canada, according to the Nepal tourism board.

Police in Nepal said 165 ⁠bodies had been recovered by late Wednesday. Chinese state media reported three dead on the Tibet side of the border.

Many of the victims were on a pilgrimage to Kailash Mansarovar, a high-altitude site in ‌Tibet that is revered by Hindus and Buddhists among others.

Early reports from Nepali ​officials initially suggested an earthquake in the area could have caused the lower part of a glacier to collapse and trigger ‌the floods. But the US Geological Survey later said what was initially reported ‌as a 4.4 magnitude earthquake was a seismic shock generated by glacial rock and ice collapsing and the flow of debris. “No earthquake had occurred.”

An initial study of Planet Labs satellite imagery indicated that a landslide of ice and rock triggered the debris-laden flood in the Lhende River, about 20km (12 miles) north-east of the Nepal-China Rasuwagadhi border crossing, Nepal’s national disaster authority said. Experts say the risk of such events is compounded by the extreme topography of the Himalayas.

In the wake of the disaster some shared harrowing stories of how they managed to survive.

“I started running. Then a wall of water came thundering down as if it was an earthquake,” said Bibek Kumal, a labourer who was working downstream from the worst-hit Rasuwa district, near Nepal’s Himalayan border with China’s Tibet.

From his hospital bed, Kumal said the torrent swept him downstream amid mud and debris but he survived by clinging to a mango tree. “Had there been no mango tree, I would ‌have been washed away to death,” he said.

“It was a huge gush of mud coming straight towards us. As it got closer, it kept rising higher and higher,” said Keshav Prasad Baral, a 68-year-old survivor, who was being treated at a small hospital.

“I tried to grab my wife’s hand and take ⁠her to the terrace. But she was swept away by the mud,” he continued. “Four or five hours later, a helicopter came to rescue me. My wife is still somewhere beneath the mud. She’s gone.”

The head of the international Red Cross (IFRC), David Fisher, said “entire villages and market areas have been wiped out”.

The UN secretary general, António Guterres, said UN teams and partners were mobilising supplies and personnel in Nepal to support communities affected by the disaster. The US government said it would provide $500,000 in emergency assistance.

Tibet government officials mobilised nearly 800 emergency workers and 150 vehicles as well as sniffer dogs and speed boats to help the rescue efforts, China’s official Xinhua news agency said. The Chinese president, Xi Jinping, said: “The most urgent task is doing everything possible to search for and rescue the missing people.”

People from the affected areas of Nuwakot and Dhading were seen gathering outside a Nepali army training centre – the base for helicopter rescue operations – seeking information about missing family members.

Police were recording the names of the missing just outside the barracks gate. Mobile phone torches were their only source of light as the area remained without electricity due to damaged hydroelectric infrastructure.

Tour company Himalayan Glacier said 47 people – including two children – were missing from one of its groups in Nepal. Among them were 15 Australians, 10 Canadians, nine Nepalese, eight Americans, two Britons, two Singaporeans, and one Russian-American dual citizen, managing director Sanket Pandey said.

The Australian prime minister, Anthony Albanese, said his thoughts were with those concerned about their loved ones, and getting information about the status of those missing remained difficult.

With Reuters and Agence France-Presse