About 40 workers at a hydropower station went missing in a rain-triggered mudslide Thursday morning in southwest China's Sichuan province, according to local authorities.

The disaster occurred at 6:14 a.m. at the construction zone of Baihetan Hydropower Station in Ningnan county, Liangshan Yi autonomous prefecture, said a spokesman with the provincial emergency management office.

The number of missing workers was initially estimated at 38 to 41, according to the spokesman.

The Baihetan Hydropower Station, currently under construction by the China Three Gorges Corporation, is located on the lower reaches of the Jinsha River, a major headwater stream of the Yangtze River, the country's longest waterway.

With an estimated gross installed capacity of over 14 million kilowatts, the station is expected to be put into use by 2020.