Water levels are expected to rise over the next three days, peaking around September 1, state broadcaster CCTV reported.

The lake formed after a wall of mud and debris hit the border hub of Gyirong in Tibet on Wednesday, with hundreds reported missing.

"According to forecasts, inflows into the lake could reach about 3 million cubic metres over the next three days amid continued rainfall, increasing the risk of a breach that could send floodwaters downstream and potentially cause further damage in areas including Gyirong Port and elsewhere downstream", state news agency Xinhua reported late Thursday.

Rain is forecast in the area over the next three days.

CCTV said that 499 local residents, as well as 555 tourists, had been transported out of the disaster zone as of Friday morning. It did not specify the tourists' nationalities.