The accident also injured three other workers seriously, who are currently receiving treatment at the Muong La general hospital, the board said, explaining that the collapse occurred when ten workers were dismantling the scaffolding at the height of 22 metres.

The Son La hydropower plant, the largest of its kind in Vietnam, is designed to have six turbine groups with a combined capacity of 2,400 MW and is expected to turn out an average electricity output of nearly 10 billion kWh a year.

In mid May, the plant closed the sluices to fill up its reservoir and planned to put its first turbine into operation safely by December 2010, two years ahead of schedule.