A massive landslide in China's mountainous southwest has dammed up a major tributary of the Yangtze river and was Friday threatening a hydroelectric dam and communities downstream, state media said.

The landslide occurred on the Dadu river in Sichuan province's Hanyuan county late Thursday, leaving two people dead and 19 others injured, Xinhua news agency reported.

It was not immediately known how many people were missing, it said.

The massive flow of mud and rocks blocked the river, leaving only a trickle flowing through to the Pubugou hydroelectric dam, the report said.

Authorities have ordered the evacuation of communities below the landslide as the backed-up water had begun to seep through the debris, escalating fears it would soon burst through and send torrents of water downstream, it said.

Torrential rain and landslides have killed nearly 70 people and left almost as many missing in south and central China since the beginning of June, state media reported last week.

On July 24, another landslide on the Dadu river engulfed makeshift housing for a dam construction crew in Shalian, leaving about 50 people missing and four confirmed dead, earlier reports said.

Parts of the Dadu river run through areas that were rocked by a huge, 8.0-magnitude earthquake in May last year that also triggered landslides in Sichuan's mountainous regions. Nearly 87,000 people were left dead or missing in the quake.