I want to visit the Intertraffic exhibition to be held in China from Sept. 07-09, 2011, how can I apply for China visa?

I am Electrical Engineer from Pakistan and working with leading Intelligent Transportation Solution Provider. My ent Visa and the ID is under process and still have not been issued. The process may take 2-3 months.

I am interested to visit this exhibition as this is directly related to my field. I am on visit visa and I got extension after every month. Would you be kind enough to guide ma as how I can apply for the visa for the China?