Hong Kong - Catholic, since there's a great population of Filipinos there which are all Catholics.
Mainland China - I'm not really sure, maybe Protestants.
China is a predominantly Buddhist country with minimal interest in Christianity. Most Christians live in Europe and former European colonies (US, Canada, Brazil, so forth). You may find Christians in Hong Kong since that city was once a British colony.
Actually, there are much more Protestants and Christian Churches in Hong Kong today than compared to Catholic. Roman Catholic Church and Catholicism is not popular amongst local Hong Kong citizens, and although it is predominantly related to Filipino's bigger religion, they are not "ALL" Catholics. Filipinos have Christian/Protestants and Muslims too.
What is more popular in China and Hong Kong; Protestantism or Catholicism?
