The director added that his administration would look into the loss of heritage sites and pledged to take action if irregularities were found.

The four-year national census of heritage sites began in June 2007, the third since the founding of the People's Republic, and it is expected to cost more than 1 billion yuan (HK$1.14 billion).

Shan said surveyors had finished nearly 90 per cent of their work on registering 776,200 immovable sites, including 550,300 new discoveries.

Professor Li Jianmin, an archaeologist at the Chinese Academy of Social Sciences, noted that most of the ruined heritage sites might yet be given official protection status, but they were valuable whether they received protection or not.

Li said the actual number of heritage sites that had disappeared could be much higher as result of what he called 'massive human plunder' - either via infrastructure development projects or theft.

An increasing number of relic-smuggling cases have been reported over the past few years. One recent case saw about 156 cultural relics smuggled to Denmark in 2006. They were returned to Beijing April last year. The relics included pottery figurines of the Tang dynasty (618-907AD) as well as rare items dating back to the Xia (2100-1600 BC), Shang (1600-1100 BC), Yuan (1279-1368AD) and Ming (1368-1644) dynasties.

On the conservation front, a more than 100-metre section of the Great Wall in the Daqing Mountain area of Inner Mongolia was destroyed in October by a gold mining company in Hohhot despite five orders from municipal heritage conservation authorities, according to mainland media reports.

Li said conservation authorities had little influence over regional governments, which often put development ahead of heritage conservation.

Conservationists have been dismayed by a shift in policies that allows them only to act as facilitator for upgrades in the name of conservation, and only when development authorities want to consult with them.

'They used to say conservation should be a primary task, but now at [the academy], we're basically not allowed to take an active role in excavation for scientific purposes,' he added.

The professor also pointed to an increase in theft of relics since the 1980s. It has become a lucrative business and given rise to a black market.

He said that police in some places colluded with the thieves, who were often allowed to go free after paying officers a fine.

Besides more law enforcement, Li said: 'To stop the disappearance of heritage sites in the future, the government must move to give the sites a higher status for better protection.'

Price of knowledge

To keep track of heritage sites, a four-year census was launched in 2007 - the third since 1949

The scheme is expected to cost (in yuan) more than: 1b