Ok you are going to have to qualify your question here. I live in China and as far as I know, people from Hong Kong are not FORCED to work in China, but many of them do. Either their companies send them into the mainland or they choose to go there themselves. The reason for this being is that the Chinese market is booming, there is a lot of money to be made here, and made in a very short amount of time. Hong Kong is known for its business, so its companies are trying to take advantage of not only the cheap labor, but the rapidly appreciating RMB (chinese currency) and the 1 billion people who can buy their goods and services. Hope that helps.

Many HK people choose to work in mainland China because their companies, although based in HK, do most of their production in the mainland. so many people who have supervisory or technical positions are needed to work in China.

Hope that helps a bit.