What triggered the catastrophic flood on the Nepal-Tibet border?

Flash floods that struck the Himalayan border region of Nepal and China's Tibet on Wednesday have killed at least 157 people. Authorities on both sides fear the final number of casualties will be far higher amid massive destruction.

Here is a look at what caused the calamity, and where things stand now.

Also read: What triggered the catastrophic flood on the Nepal-Tibet border?

WHAT HAPPENED?

On Wednesday morning, the lower ‌part of ⁠a glacier ⁠in the Himalayas collapsed and crashed onto the valley floor, possibly triggered by an earthquake. ​An avalanche of ice and rock swept down the Lhende Khola river, which runs ​along the mountainous Nepal/Tibet border.

The mudslide slammed into Gyirong port in Tibet and into Nepal, creating high-speed flash floods that washed away entire roads and power ​projects and inundated villages.

HOW MANY ARE DEAD AND ⁠MISSING?

Authorities have ‌recovered 157 bodies so far, but the death toll ​is expected to ​rise sharply. It is unclear how many overall are ⁠missing.

The missing reportedly include over 400 foreign visitors, including 133 ​Indians on a pilgrimage, 47 Americans, 34 Australians, 33 ​British and 24 Canadians. Nine South Koreans working on a hydropower plant are unaccounted for, and citizens of Malaysia and South Africa were also reported missing.

About 5,000 people were evacuated in the Indian state of Bihar after flood alerts were issued.

Also read: India dispatches first relief aid to flood-hit Nepal

WHAT IS THE SITUATION NOW?

Police and military personnel are ‌conducting rescue efforts, although officials have said rescue helicopters will not be able to land in some of the affected areas ​until the waters ​recede. Much of ⁠the area is without electricity and flood sediment is posing a challenge.

People living in low-lying regions have been moved to safer places, and those along the ​river have been advised to remain alert.

The United Nations has said it is mobilising supplies and personnel to support affected communities. India said it was coordinating closely with Kathmandu on rescue and relief efforts, and South Korea is sending a rapid-response team.