Where is the Chinese wealth from?

It's been argued that the PRC is buying up the whole world. The spending power of the mainland Chinese businessmen, investors, tourists, students, etc. has been steadily increasing throughout the past three decades.

I know the economic boom has to do with the Dengist economic reform (so state policies), but I'm still wondering WHERE do all these money come from? China is not particularly rich in natural resources; it's not a mature financial power; so where on earth can people find their capital in such a short period of time?