F*ck You. Pay Me. http://vimeo.com/22053820
In China, if you have an ironclad contract and no other leverage, you have no leverage.
In cases such as this, it's best to take payment up-front for a portion of the work, either in the form of a deposit (for fixed-bid), or a retainer (for hourly work).
This means you get money up front, which is nice. More importantly, you get something I like to call fiscal inertia -- namely, if a client has paid once, they're far more likely to pay in the future.