Experts involved in preservation work told Xinhua news agency they had discovered significant interior damage to the wall, considered one of the best preserved ancient city fortifications in the country.

'The mites had lived and built their dens in the wall for a thousand years, and had eaten it away from the inside,' it quoted Mr Li Yuhu, an archaeologist working on the wall, as saying.

The damage was discovered at one of the 18 gates, each of them eight metres high, that lead through the wall and into the centre of Xi'an, now the bustling capital of Shaanxi province in northwestern China.

Experts have begun treating affected areas with a non-toxic insecticide and then shoring up the wall with a specially developed mite-resistant material.

Xi'an is famed for a number of historical sites, most notably the world famous terracotta warriors found in the tomb of China's first emperor, a short drive from the city. -- AFP