Nepal-Tibet disaster: what we know

Catastrophic flooding and landslides on the Nepal-Tibet border unleashed waves of water and debris that killed at least 180 people and left hundreds more missing.

Here is what we know so far:

The exact sequence of events is still unclear, but on Wednesday morning, torrents of water and debris crashed downstream on both sides of the border.

Surveillance video from the Chinese side showed a wall of mud and water crashing over a building as terrified people ran away.

In Nepal, a surge of water hit villages and towns on the path of two rivers -- Bhote Koshi and Trishuli.

The disaster was intially described as a flood on the Nepali side, and a mudslide by Chinese authorities.

At least 180 people have been reported dead, 177 in Nepal and three in Tibet.

Chinese authorities have said the disaster caused "major casualties" and reported another 558 missing -- 260 of whom are foreigners.

On the Nepali side, authorities said Thursday that 468 tourists, 393 of them foreigners, were unaccounted for.

The missing include Indians and others from Ukraine, Malaysia, the United Kingdom, South Africa and elsewhere.

Australia said 34 of its citizens were missing in Nepal.

Another 93 Nepali citizens have also been reported missing.

Some 77 pilgrims from across the world were at the Nepal-China border immigration office when the flood hit on Wednesday, popular Indian spiritual leader Sadhguru said.

Promises of aid and assistance came in soon after reports of the scale of the disaster.

The United States has pledged $500,000 in emergency assistance, and the International Federation of the Red Cross and Red Crescent Societies released $1.4 million.

"The priority now is to reach affected communities and get assistance to people who have lost their homes, suffered injuries or have been cut off," its Nepal head David Fisher said.

The European Union said it had activated its Copernicus satellite surveillance system to help recovery efforts and was ready to provide more help, while the World Health Organisation said it had dispatched emergency medical supplies.

Neighbouring India has sent an initial 10 tonnes of humanitarian assistance.

The explanation for the calamity has evolved since it struck, but appears linked to a collapsing glacier.

Within hours of the flooding, Nepal's Foreign Minister Shishir Khanal said an earthquake likely triggered a landslide, in turn blocking a river and sending water gushing downstream.

China also reported a landslide, saying a border hub between Tibet and Nepal had been hit by a surge of debris.

The Nepali foreign minister's statement aligned with a US Geological Survey report of a quake in Tibet that was north of the disaster zone.

However, USGS subsequently updated its conclusion to say the seismic activity initially reported as a quake "was instead a glacial collapse and debris flow" that "caused subsequent catastrophic impacts downstream".

"Additional analysis of nearby seismic stations, long period seismic waves, and satellite imagery led to the determination that the seismic event was instead a glacial collapse and debris flow, and that no earthquake had occurred."