Chinese government statistic show that nearly 30 percent of China's land mass is covered by desert, and the desert is growing.  Environmentalists say the loss of farmland to desertification affects the livelihoods of millions of people, and has a severe impact on China's economy. Sam Beattie reports.

A rustic fence is no match for the relentless movement of sand into farming areas of western China

The Kumtag is China's sixth largest desert.  And state media reports it is creeping closer and closer to the city of Dunhuang in China's far West -- creeping at a rate of between one and four meters each year. Ninety percent of the city has already surrendered to desertification.

This highlights a growing problem in China -- large tracts of land in the country's arid western provinces are turning from farmlands into deserts.

Mayor Sun Yulong says he is doing all he can to protect his people. "We recognize the importance of the environment.  For example, it is forbidden to dig a well and take water from under the ground. We are reducing the farming lands to protect the water resources under the earth, and we are also planting trees in heavily affected regions."

Environmentalists say desert expansion has accelerated across China since the 1950s.  Deforestation, livestock overgrazing and inefficient water use have all compounded the problem.  In Dunhuang, the desert grows as farmers draw water from underground reserves faster than nature can replenish them.

Cotton farmers work their fields near He Shui Village in western China as massive sand dunes move ever closer

Environmentalist Chen Jiqun says now it is nearly an irreversible process. "It's hard to restore the original vegetation because there is very little water.  You cannot plant anything where there is no water."

The government has launched large-scale tree planting campaigns to halt the desert's movements with varied success.

Farmer Ma Yuzhen has spent her whole life working these lands. She knows the difficulties of keeping the sand dunes at bay. "The sand is moving little by little. It is not hazardous to our health, but we worry what will happen if there is no more land to cultivate. We will not be able to live here any more.  All we can do is to plant trees and try and stop the sand moving."

China's State Forestry Administration says the advance of the desert results in a direct annual loss of billions of dollars, while threatening the livelihoods of some 400 million people. But it is not just a problem for remote farmers.  The Gobi Desert stretches from Mongolia to within 240 kilometers of Beijing.