Shenzhen-based Tencent Holdings, one of the largest technology companies in the world, is building out a data center inside a mountain in rural Guizhou.

The new data center will house tens of thousands of servers and provide secure storage for WeChat data, among other Tencent data requirements.

Construction on the Guian Seven Stars Data Centre complex, Tencent’s largest data storage facility, began last June. The 51-hectare site includes 30,000 square meters of tunnels inside a 100-meter high hill. Data will be stored in a large cavern inside the hill, which has been built to house Tencent’s servers.

The interior location will help Tencent take full advantage of the local climate, to create an effective, natural cooling system to supplement power and cooling for the data center. Access to the facility will be provided by the five round, cavelike entrances that have been bored into one side of the hill. A recent China Central Television report showed video footage of metal gates installed at these entrances, and noted that the gates were built to national standards for civil air defense, effectively turning the data center into a bomb shelter.

While the mountainous, rural province of Guizhou has traditionally been less-developed than other Chinese provinces, it has become a key part of the high-tech industry in China. In 2014, the government of Guizhou province began to offer incentives to attract companies including big data, internet, cloud, and data centers.

The province is particularly appealing to data center operators due to the cool climate, inexpensive land, cheap hydropower, and low risk of natural disasters such as earthquakes.

Last summer, when construction began on Tencent’s Seven Stars complex, Huawei, Foxconn and Apple each began construction on enormous data center facilities of their own in Guizhou.

Foxconn built a factory as well as a 500,000 square foot data center near the provincial capital of Guiyang. Last August, Huawei began construction on a 400,000 square meter facility built to accommodate up to 600,000 servers. Just prior to that, Apple announced a $1 billion USD investment programme for Guizhou province, including the construction of a data center that could support over 92,000 square meters and 150 MW capacity.

Apple’s decision was made, in part, to comply with the Chinese government’s legislation requiring in-country storage of Chinese data.