A view from inside Boniu Sinkhole, one of the large ones in nearly 50 sinkholes discovered in Shaanxi province, Northwest China. Most of them are well preserved in such counties as Ningqiang, Nanzheng, Xixiang, Zhenba, Gucheng and Mianxian. [Photo provided to China Daily]

After a four-month survey last summer, geologists confirmed that 49 sinkholes had been discovered in the mountains near the city of Hanzhong in Northwest China's Shaanxi province.

"Sinkholes are a rare geological phenomenon. To find this many sinkholes together is unprecedented," Li Yichao, a senior engineer at the Shaanxi Geological Investigation Institute, told Xinhua reporters.

In fact, before the Hanzhong sinkholes only 130 such sinkholes had been found worldwide. All the previously discovered sinkholes are located between latitude 24 to 31 degrees north. Yet the Hanzhong sinkholes are located near latitude 33 degrees north.

"It is a miracle in world geological history," said Zhang Yuanhai, a researcher at the karst geology institute, affiliated to the Ministry of Land and Resources. "No one ever expected there to be sinkholes this far north and we need a lot of research to know why they are here."

Located in Qinba Mountain in the province, the Hanzhong sinkholes comprise one super large sinkhole, 17 large sinkholes and 31 conventional sinkholes.