Archaeologists and engineers are working to restore protective eaves and attics to the 15,000-year-old Yungang Buddhist Grottoes, a world heritage site in northern Shanxi Province, to slow down its weathering.

The restoration is to take two years and cost roughly 50 million yuan (7.69 million U.S. dollars), said Zhang Zhuo, head of Yungang Grottoes Research Institute. He said the grottoes are facing serious threat of erosion as most of the original protective eaves have been damaged over time.

Engineers will first work on six most-damaged grotto caves, where some of the grotto columns are likely to collapse, he said.

The Yungang Buddhist Grottoes in Datong City boast 51,000 Buddhist images in 53 caves stretching for one kilometer along a cliff. The carving of the grottoes started 1,500 years ago. It was listed as a UNESCO World Cultural Heritage site in 2001.