Thousands of Chinese and Japanese volunteers have taken part in an on-going Sino-Japanese experimental program to prevent a desert in north China from expanding with eco-friendly bags.

"The bags are made of corn hull, a by-product from corn processing. They will naturally degrade in six years without harming the environment," said Wu Jingzhong, a Chinese representative of the Japan-based World Desert Reclamation Association.

The Japanese side has promised to donate a tonne of the corn hull bags to help build the barrier on the eastern edge of the Tengger Desert, the fourth largest in China.

More than 5,000 Chinese primary- and middle-school students as well as 1,500 volunteers including 500 from Japan have helped fill the sand bags.

The sand-bag barrier is being built between the desert edge and a 50-km green belt, created over the past seven years in programs between the local government of the Alxa League in north China's Inner Mongolia Autonomous Region and the Japanese association.

The League, located on the western end of Inner Mongolia, has one third of its 270,000 square km of land covered by three deserts. It has become one of the three major sources of sandstorms in China.