Chinese government report recommends the relocation of an extra 300,000 people at risk of landslides and water pollution

A further 300,000 people must be relocated from around China's Three Gorges dam - in addition to the 1.2 million who have already been forced to leave their homes, according to a draft government report.

Less than two years after completion of the world's biggest hydroelectric power plant, site engineers have found landslides and water pollution are more severe than anticipated, prompting calls for drastic remedial efforts.

In a report drawn up over the past year, the managers of the project and regional officials recommend the withdrawal of people from long stretches of the reservoir's banks.

"We aim to decrease the human impact on the environment and restore the ecosystem," an official familiar with the report told the Guardian. "It will be hard because the plan will cost a great deal of money and involve finding new homes for many people."

The report - entitled the Three Gorges Follow-Up Project - is still being considered, but given the input from senior levels of central and local governments, its recommendations are highly likely to be followed.

Since the start of construction in 1992, about 16m tonnes of concrete have been poured into the giant barrier across the Yangtze river, creating a reservoir that stretches back almost the length of Britain and drives 26 giant turbines.

But the rise and fall of such a huge volume of water has triggered land slides in the surrounding area, while the slowing of the flow has made it more difficult to flush pollution from the river system. Planners hoped the hydrological situation would stabilise by itself, but they are now calling for additional measures.

"An eco-screen, or buffer belt, is waiting for approval to be built alongside the reservoir to improve the water quality of the Yangtze river streams and reduce the contamination from residents living nearby," Hu Jiahai, a deputy of the local people's congress, told the China Daily.

He said the State Council - the Chinese cabinet - was now considering the relocation and other proposals, which were likely to cost at least as much as the 40 bn yuan (£3.7bn) already paid in compensation to those moved for the project.

Finding new homes for so many people will not be easy in an area that has already experienced mass migration and overcrowding. According to the state media, the population density in the reservoir area is already more than twice the nation average.

But this may just be the start of remedial efforts. The report predicts the problems of landslide and river-bank collapses will continue for 20 years, prompting even greater relocations. Last year, senior officials quoted in the newspaper 21st Century Business Herald anticipated a need to move 5 million people.

Overseas environmental protection groups called on the government to learn from the errors of past resettlement programs.

"Compensation must be sufficient for affected people to buy their new homes and invest in a new economic future. Affected people must be allowed to protest abuses [of power], and corrupt officials must be systematically held to account," said Peter Bosshard of International Rivers. "Future dam projects must be evaluated more thoroughly."