China has finished evacuating the last town to be submerged by the giant Three Gorges Dam, making way for water levels in the reservoir to rise to their final height of 175 metres above sea level, state media said.

The final residents of Gaoyang in central Hubei province left on Tuesday, the end of an exodus that began four years ago, the official Xinhua agency reported.

In total, some 1.4 million people have been moved to make way for the waters behind a 2,309-metre-long dam, the world's largest hydroelectric feat. It aims to tame the Yangtze River and provide clean, cheap energy for China's rapid development.

Critics of the dam say that pollution and geological threats are piling up. Scientists have said that rising waters in the 660-km (400-mile) long reservoir have strained already brittle slopes, triggering landslides, which may worsen when waters reach a maximum height.

A big mudslide hit a village in the Gaoyang area in April, sweeping into the local school's playground and part of the village. And a landslide nearby killed 35 people late last year.

But officials said last year that 12 billion yuan (882 million pounds) had been allocated over past years to "geological repairs", and they were confident that such efforts were working.

Finished in 2003, the water level has risen in stages, reaching 156 metres in 2006. It is expected to reach its final height next year.