China's Three Gorges Dam, the world's largest water control project, has begun generating electricity.
The first of the dam's 26 generators to go into operation was connected to the power grid at 0131 local time on Thursday (1831 GMT on Wednesday), 20 days ahead of schedule, Xinhua news agency reported.
China says it badly needs the electricity the dam will generate
The generating unit will supply 12.9 million kWh per day to the power grids in central and east China, the project's vice general manager said.
Yang Qing said the unit would have to pass a 30-day trial operation, before beginning commercial production in August.
The combined energy of all the dam's 26 generators will eventually generate more than 80 billion kWh of electricity each year.
The Three Gorges dam is unprecedented in both the scale of its construction and the number of people who have been forced to move to make way for the project.
By the time it is completed, the water level will reach a depth of 175 metres (574 feet), and create a reservoir which is 600 kilometres (375 miles) long.
Many villages and towns - and even some small cities - along the banks of the densely populated Yangtze have already been submerged by the rising waters.
More than 600,000 people have been forced to relocate, some as far away as Shanghai, 1,000 km (600 miles) east. About 1.3 million people will eventually have to move.
China's leaders say the country needs the 180bn yuan (US$22bn) dam to produce electricity, as well as control the annual flooding of the Yangtze.
But critics are worried about the destruction of dozens of cultural heritage sites.
And they say that if the dam breaks, it would spell disaster for those living down-river.
Many environmentalists have also warned about the danger of soil erosion, as well as pollution caused by trapped sewage and industrial waste.