Hong Kong, still maintaining a degree of independence from Mainland China has separate immigration laws. As a legacy from the British rule and fitting into its image as an international city many western visitors do not need to obtain a visa in advance. However if you wish to visit Mainland China, or Macau you will need to get a different visa.

For up-to-date detailed information on current visa requirements visit: http://www.immd.gov.hk/ehtml/hkvisas_4.htm