[Photo provided to China Daily]

According to Zhang Shuanhou, a senior engineer at Shaanxi Geological Investigation Institute, a sinkhole is "large" if its diameter is between 300 and 500 meters, and "super large" if its diameter is more than 500 meters. The largest Hanzhong sinkhole has a diameter of 520 meters and it is 320 meters deep at its deepest point.

The cluster was first discovered in February 2015 by a national geological exploration team. The team, including experts from the UNESCO International Research Center on Karst, the International Union of Speleology and research bodies of Czech, France and China, then jointly surveyed the region last year.

The expert panel agreed the Hanzhong sinkhole cluster is rare, complete and spectacular in landscape, Wang Weihua, director of Shaanxi Provincial Department of Land and Resources, said after the team had completed its survey.

More importantly, these geological rarities are so far intact.

"The Hanzhong sinkholes are one of the most well-preserved natural geological phenomena in the world," Zhang said.