The 36 billion yuan (US$4.9 billion) project in the Aba Tibetan and Qiang autonomous prefecture, in Sichuan province, has been under construction for nearly a decade and will be used for power generation and flood control.
It is situated upstream of the Dadu River, which flows from the eastern Tibetan Plateau into the Sichuan Basin.
State-owned Power Construction Corporation of China (PowerChina) is building the project – the dam, a diversion and power generation system, as well as flood discharge structures.
When finished the dam will be 315 metres (1,033 feet) high – about the same height as a skyscraper with more than 100 storeys and 10 metres taller than the current record holder, the Jinping-I dam, also in Sichuan.
PowerChina said in a statement on Tuesday that the water level was at 2,344 metres after the first phase of water storage was completed – about 80 metres higher than the original river level.
