China's archaeologists are as a matter of fact playing a risky cat and mouse game with tomb robbers who are destroying and stealing national treasures and are often just one step ahead of the police.

Archaeologists report a third of China's 400,000-plus archaeological sites have been hit by thieves and that half of the country's top-ten ancient discoveries in 2005 had been at least partially looted.

Although local police are often asked to patrol the ancient tombs they have had little effect, said archaeologists.

In a number of cases, Chinese archaeologists find themselves following the robbers' trail and end up only being able to salvage what has been left behind by the thieves.

The excavation to the 3,000-year-old tombs, which belonged to the royal family of Western Zhou Dynasty (1100 BC-771 BC), in Jiangxian County of north China's Shanxi Province, is one example.

Song Jianzhong, deputy director of the Archaeological Institute of Shanxi Province, said that after hearing that tomb robbers were active in the county, archaeologists rushed to the scene. They managed to excavate 191 of the most endangered tombs, but they were too late to save some of the most valuable artifacts. "Eleven of the tombs had been looted. In one we found bronze ware wrapped in newspaper that robbers didn't have enough time to take away," said Song.

"We found nine holes in the tomb left by the robbers. This means there could have been three or four groups of robbers here in the past two years," Song said.

Song estimated there are more than 300 ancient tombs at the site, and over 100 have not been excavated. He's worried about the safety of the other tombs.

"Although armed police were safeguarding the site during the excavation, the tombs that have not been excavated are still in danger of being robbed after the archaeological team leaves," Song said.

The archaeological digs in the provinces of Guizhou, Shanxi, Shaanxi and Jiangsu were all honored by experts this week and all had been looted to some degree.

"Many beautiful antiques have been stolen by the robbers. The interior structure of the ancient tombs have been ruined and we've lost some crucial historical information," said Lin Liugen, head of the archaeological team conducting excavation to the tombs in east China's Jiangsu Province.

Of the 25 nominees for last year's top 10 archaeological discoveries, ten have been damaged and looted over the last two years, acknowledged archaeologists.

Ace Chinese archaeologist Zhang Zhongpei said the robberies pose a serious threat to China's cultural heritage. He blames people's ignorance, and corruption.

A census conducted some 20 years ago showed that there were more than 400,000 historical sites across China. Experts now estimate at least a third of them have vanished over the past two decades as a result of human destruction.

Shan Jixiang, Director of the State Administration of Cultural Heritage, has proposed setting up a special police task force that would be in charge of protecting the relic sites.

Experts also say that a new census should be conducted to determine the current situation of archaeological sites across the country.