ICRAS 2017 - Hong Kong
Nationals of about 170 countries and territories may visit Hong Kong visa-free for a period ranging from 7 days to 180 days. Check this webpage to learn whether you need a visa or entry permit to enter Hong Kong:
Guidebook for Entry for Visit/Transit in Hong Kong:
Letter of Invitation:
A Letter of Invitation is a proof that your paper submission and registration application are accepted by the conference committee board. It perhaps could help with your visa application. However, it does not guarantee you a visa.
The invitation leter will be issued ONLY after you have registered and full payment has been received.