Catastrophic floods and landslides along the Nepal-Tibet border have killed at least 165 people and left hundreds more missing.

The disaster struck on Wednesday morning. Powerful torrents of water, mud and debris swept through communities on both sides of the border.

Here is what is known so far:

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What Happened?

The exact sequence of events remains unclear.

On the Chinese side, surveillance footage showed a wall of mud and water crashing into a building as people ran for safety.

In Nepal, floodwaters swept through villages and towns along the Bhote Koshi and Trishuli rivers.

Nepalese authorities initially described the disaster as flooding. Chinese officials said the area had been hit by a mudslide.

Hundreds Missing as Death toll Rises

At least 165 people have been confirmed dead. Nepal has reported 162 deaths, while three people have died in Tibet.

Chinese authorities said the disaster caused major casualties. They also reported 558 people missing, including about 260 foreigners.

In Nepal, authorities said 468 tourists remained unaccounted for as of Thursday. Of those, 393 were foreign nationals.

The missing include people from India, Ukraine, Malaysia, the United Kingdom and South Africa.

Australia said 34 of its citizens were missing in Nepal.

Another 93 Nepalese citizens have also been reported missing.

International Aid reaches Affected Areas

Countries and international organizations have started providing emergency assistance.

The United States pledged $500,000 in emergency support.

The International Federation of Red Cross and Red Crescent Societies also released $1.4 million for relief efforts.

Nepal head, David Fisher, said the immediate priority was reaching affected communities and helping people who had lost homes, suffered injuries or been cut off.

The European Union activated its Copernicus satellite monitoring system to support rescue and recovery operations.

The World Health Organization also dispatched emergency medical supplies.

Neighboring India sent an initial 10 tonnes of humanitarian assistance.

Glacial Collapse Emerges as likely Cause

Initial reports suggested the disaster may have been triggered by an earthquake.

Nepal’s Foreign Minister Shishir Khanal initially said an earthquake may have caused a landslide. The landslide was believed to have blocked a river before releasing a massive surge of water downstream.

Chinese authorities also reported a landslide near a border hub between Tibet and Nepal.

The theory initially appeared consistent with a US Geological Survey report of seismic activity north of the disaster area.

However, the USGS later revised its assessment.

It said the seismic event was not an earthquake. Instead, analysis indicated that a glacier had collapsed, triggering a debris flow and catastrophic flooding downstream.

The agency said its conclusion was based on further analysis of seismic stations, satellite imagery and seismic waves.