2019 Summit Visa and Passport Requirements
All visitors to Hong Kong must have a passport that is valid for at least one month to six months (depending on nationality) after the period of their intended stay in Hong Kong. If you want to travel from Hong Kong to mainland China, you may need to apply for a Chinese visa. It’s recommended that visitors check current regulations with the Hong Kong Embassy.
Delegates holding passports from many countries, including Australia, Canada, Europe, New Zealand and the United States, are not required to have a visa to enter Hong Kong for stays of 90 days; United Kingdom nationals can stay for six months without a visa.
A full list of countries, including visa requirements, can be found at this link (click on Part II).