The massive wave of mud and debris swept into Tibet's border hub of Gyirong on Wednesday, killing at least seven people and leaving 554 missing in that area, according to figures published early Saturday by China's Xinhua news agency.

More than 500 rescuers had reached the heart of the devastation by Saturday, the agency reported.

Rescue operations had been temporarily paused because of the threat of renewed flooding from a lake formed by the mudslide. But state broadcaster CCTV said late Saturday that the lake was "discharging naturally" and had been "essentially drained", citing China's ministry of water resources.

The US Geological Survey said the disaster on the Tibet-Nepal border was caused by a glacial collapse that sent a torrent of debris downstream.

While the exact cause of the collapse is unclear, climate change is causing glaciers to melt worldwide, increasing the risks of such disasters.

Rescue efforts in Tibet continue to be hampered by rain, the closure of access roads and rugged terrain.

Footage aired by CCTV showed helmeted firefighters crossing treacherous waters in inflatable boats or being airlifted one by one to the other bank by a powerful drone.

It also showed excavators and bulldozers attempting to reopen access routes.

The weather service forecast light to moderate rain across most of the area until Sunday.

A total of 2,141 rescuers were near the Gyirong site, Xinhua reported, including the more than 500 in the worst-hit area.

On Friday, 499 Chinese nationals and 555 foreigners were said to have been transported out of the disaster zone in southwestern China.

Chinese officials have put the number of foreigners missing in Tibet at 260.