TOEFL and IELTS are both fine! However, IELTS will be relatively easier, and TOEFL is a machine test, which many students in China are not very used to!

TOEFL or IELTS, is a must! Hong Kong Baptist University, City University of Hong Kong, and Hong Kong Polytechnic University can theoretically apply with CET-6, but if the research background is not very strong, it is still recommended to take IELTS or TOEFL.

About GRE, Hong Kong universities don't really have a hard requirement for GRE, but many faculties of the Hong Kong University of Science and Technology require GRE, and in addition, GRE is preferred for business schools.

Development:

On January 15, 2019, China's Ministry of Education's Examination Center and the British Council for Culture and Education jointly released the results of a study on the interface between IELTS and P&E exams and China's English proficiency scale in Beijing. Scale docking research results, marking the convergence of China's English language proficiency standards with international exams, and a new stage of Sino-British cooperation in the field of education.

The results show the critical scores for each skill and total score of IELTS and PTS corresponding to the relevant levels of the Chinese English Proficiency Scale (CEPS). For example, a score of 5 for IELTS Listening means reaching the level 4 of the Chinese English Proficiency Scale; a score of 5.5 for Reading means reaching the level 5; a score of 6 for Speaking means reaching the level 6; and a score of 8 for the overall result means reaching the level 8, etc.

Reference: Baidu Encyclopedia - IELTS