* A baby bust left over from the introduction of the one-child policy, at which point its dependency ratio will skyrocket to levels unmatched in any other industrialized country. One phrasing I've heard is that China needs to get rich before it gets old
* Environmental damage that takes money to reverse (that is, to reverse while maintaining living standards). Environmental damage in the sense of damage to the urban environment that industrial workers live in, not just to wilderness areas - unbreathable air, toxic rivers, etc.
* A large rural population whose urbanization is unstoppable, and whose urbanization needs to be supported by jobs and housing to avoid the kind of slums you see in e.g. Brazil or Nigeria and attendant civil disorder. Which brings us to:
* An autocratic political system whose popular legitimacy is built on economic growth, and whose popularity will (in the eyes of the people running it) collapse if it can't deliver truly spectacular economic results.