The disaster took place at the construction zone of Baihetan Hydro-power Station in Ningnan county, Liangshan Yi autonomous prefecture, a spokesman with the provincial emergency management office said.
The number of missing workers was initially estimated at 38 to 41, state-run Xinhua quoted the spokesman as saying.
The Baihetan Hydro-power 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 ready by 2020.
