A picture of China's Tianlongshan Grottoes in Taiyuan, capital of North China's Shanxi province, Aug 12, 2013. [Photo/VCG]

China's Tianlongshan Grottoes have reopened to public after two and a half years of renovation, authorities in Taiyuan, capital of North China's Shanxi province, announced Thursday.

"Before the renovation, the grottoes were threatened by falling rocks and rain erosion," said Chai Ruhui, who was in charge of the project.

According to the site's administrative office, rocks surrounding the grottoes have been reinforced and cracks have been filled with cement. Workers also dug gutters on the top of caves to protect them from rain erosion.

Walkways and guard rails have been rebuilt to protect visitors.

The renovation project, with a total investment of more than 10 million yuan ($1.5 million), started from November 2014 and was completed in June this year.

Cultural relics authorities have checked the renovations and confirmed it can be reopened to the public, according to Guo Baoping, deputy director of the site's administrative office.

Construction of the Tianlongshan Grottoes, notable for its Buddhist statues, began in China's Northern Wei Dynasty (534-550). The site contains 25 caves built during five Chinese dynasties.