During his visit to China, the US President, Bill Clinton, will view the army of terracotta warriors at Xian.

BBC correspondent Colin Blane reports on how China's past is being plundered

The 6,000 figures, unearthed in 1974 by peasants digging a well, are preserved in good condition and are recognised as being among the world's greatest historical treasures. But not all of China's heritage is as well protected.

Across the country cultural relics are being legally or illegally unearthed, dusted off and sold to unscrupulous dealers.

Despite laws that prohibit the export of objects aged 100 years and older, a market in ancient artefacts is thriving inside China.

Archaeologists fear vital historical clues are being lost

Many of the most precious objects find their way out of the country, often via transit points such as Hong Kong.

This means that the authorities and historians face huge problems safeguarding artefacts that may throw light on how people have lived in China for thousands of years.

According to the Xinhua news agency, customs officers in China uncovered 2,322 cases of smuggling in the first five months of 1998 - up nearly 10% over the corresponding period of last year.

The captured contraband included 986 ancient relics as well as drugs, pornography and counterfeit money.

Objects aged 100 years or more are not allowed to be exported

However, the true scale of antiquity smuggling is likely to be much larger. British customs recently intercepted and returned a shipment which included 3,000 vases and other objects.

Lyndel Prott, a member of the cultural division of the United Nations Educational, Scientific and Cultural Organization (Unesco), says that seizure illustrated the harm that smuggling can do.

"A lot of damage had been done to that material," she said.

"Even more serious was the loss of context. We don't know where they came from, which province, which ancient burial site."

Mrs Prott was one of the international experts recently invited by China to its first ever conference devoted to finding ways to combat the illegal trade.