The ground level of the Guanyin Cave gives visitors a temporary place for relief and awe at deeper wonders. [Photo provided to China Daily]

Sinkholes must be one of the rarest geological phenomena in the world, since they are formed when carbonate rocks are eroded over a long period of time by an underground river, the water would hollows out the rock which eventually collapses, leaving the process up to 500,000 years to form.

"The Hanzhong sinkholes are by far the most northern karst geological form in China," Liu Tongliang, director of karst geology institute, affiliated to the Ministry of Land and Resources, was quoted by cnwest.com. "They are of great significance to geology and the study of historical climate changes."

The Hanzhong sinkholes are important for other scientific research as well. Being unknown to the outside world for so long, they have been left untouched by human progress character, thus a unique habitat for plants and animals.

The biodiversity in the sinkholes is far more complicated than might be imagined and experts expect to find new species here, he said.

In March, when a joint research team of China and France visited a sinkhole in Donglan county, Guangxi Zhuang autonomous region, South China, they found various kinds of unidentified animals and plants.

The Hanzhong sinkholes are expected to be another rich treasure trove of biodiversity.