XINING -- Police in Northwest China's Qinghai province have caught 13 suspected tomb raiders and retrieved more than 400 cultural relics, according to local authorities.

The suspects were caught early on Saturday in Xining city and Dulan county, according to the provincial public security department.

They were suspected of illegal excavation of tombs in Dulan, some of which date back to between the 7th and 8th century.

Experts believe many of the retrieved cultural relics have tremendous value, said Bai Shide, deputy head of the department.

Police are investigating the case.

Dulan is home to more than 2,000 tombs dating back to the Tang Dynasty (618-907), where silk, gold, silver, bronzeware and other items have been unearthed since 1982.