Hongkong Visa Requirement for Transit Passengers at Hongkong Airport

I am a Pakistani passport holder having South Korea Alien Registration Card valid upto 25th February 2012. I plan to travel from Seoul to Karachi (Pakistan) end Devember 2011/January 2012 by Cathay Pacific Airline. The flights are from Seoul to Hongkong, transit at Hongkong Airport and then take Hongkong to Karachi flight. As a transit passenger not leaving the airport I should not require Hongkong visa. Request to please clarify.