The deets, according to 9to5Mac, involve a site on the Hong Kong side of the Shenzhen China border.
We spoke to a bidding contractor employee who, on the condition of anonymity, told us the planned data center's scale is unprecedented for his business: "There is simply nothing to compare it to and therefore it is hard to make estimates on size based on the materials required." We were told that construction is to begin in Q1 2013, and it will likely take over a year for operations to start in the data center. The aim is to have it operational by 2015, which is the same time that Apple's Spaceship Campus 2 is scheduled to go online.
On the surface, there's a good business reason for such a move, given the accelerating use of smartphones in China, which passed 1 billion users earlier this year. Apple already operates several data centers in the U.S. There's also a good security reason as Seth Weitraub correctly notes: putting the data center in Hong Kong may make it harder for Chinese government snooping.