Cigarettes Traveling to Mainland China but through Hong Kong

I'm traveling to mainland China but planning to take a plane from JFK to Hong Kong. Then from Hong Kong, I will take a high speed rail to mainland. I would like to bring some cigarettes for relatives, so I am wondering what is my limit. I looked online that China duty free allows 400 cigarettes but Hong Kong only allows 19. Does this mean I am only limited to 19, or else I would need to pay duty in HK?