Torrential rains in mountainous southwest China triggered a mudslide that left about 40 workers building a hydroelectric dam missing on Thursday, state media reported.

The mudslide occurred overnight Wednesday in Sichuan province's Ningnan county and as of midday (0400 GMNT) Thursday rescue workers were unable to contact the work camp housing the construction team, the Sichuan Daily said.

The mudslide was at the construction site of the Baihetan hydroelectric dam on the upper reaches of the Yangtze river, China's longest, the report said.

Rescuers were immediately dispatched in hopes of reaching the site where between 38 and 41 workers were living, it said.