Visas are not required for short-term visitors from the following countries: U.S.A., Canada, Britain, France, Germany, Spain, Italy, Philippines, Thailand, Japan, South Korea, Singapore, India, Israel. Visitors from other countries should check with their local consulates.

Visas are required for non-Chinese passport holders. If you wish to visit mainland China you should apply for a visa at a Chinese embassy or consulate in your country of residence. To apply for a visa you will need a valid passport, a passport-sized photograph, and a completed application form. There is no visa processing charge for visitors from the U.S.A. but there is a charge for visitors from most other countries.

For more information, please visit the links below : 
 
Visa / Entry Permit Requirements for Hong Kong
http://www.immd.gov.hk/ehtml/hkvisas_4.htm