But it warned the country's long-term development remains threatened by environmental, economic and social damage from expanding deserts -- especially in frontier lands dominated by ethnic groups such as Tibetans and Uighurs.

"Rampant firewood gathering, land reclamation and grazing, as well as shortages of water resources and their irrational use, are quite serious problems, and the task of holding back and repairing deserts remains extremely arduous," it said in an official decision issued by the Xinhua News Agency.

Problems created by expanding deserts lead to 50 billion yuan of direct economic losses every year, the document said.

But it promised that by 2010 China will establish "clear improvements" in key areas, and by 2020 half of the country's desertified land that can be repaired will have been.

The decision said local officials will be made responsible for desert repair efforts in their areas, and the central government will declare vulnerable terrain off limits to all development.

Farmers and herders in those areas will be resettled.

Deserts now occupy 1.74 million square kilometres of China, or 18.1 percent of its land, it said. It said close to 400 million Chinese are affected by the problem, but did not specify how.

In recent years, after severe dust storms whipped Beijing and other cities, China has taken action to halt spreading deserts, especially in its north and west where the Gobi Desert has displaced herders and farmers.

Areas under threat from encroaching desert sands will be planted with grasses and trees, land development in vulnerable areas will be banned, and local officials must enforce bans on digging for lucrative medical herbs, the announcement said.

The size of sheep and cattle herds that graze on vulnerable grasslands will also be "strictly controlled," it added.