Navigation trial at the Three Gorges Dam, 30 April 2007

China's state media report the environmental impact of the Three Gorges Dam project may force four million more people to relocate from the area.

Friday's reports say residents near the dam will be encouraged to move to the outskirts of the nearby city of Chongqing in southwestern China. Nearly 1.5 million people have already been displaced to make way for the world's biggest hydroelectric project.

The reports quote Chongqing's Vice Mayor Yu Yuanmu as saying the reservoir area near the dam has a vulnerable environment that is threatened by overpopulation.

Last month, Chinese media reports said the project had created potentially catastrophic environmental problems, including flooding and land erosion.

Environmentalists, who have long condemned the project, say the dam's reservoir will likely become heavily polluted with industrial waste.