Originally Posted by
tauphi
You can obtain a green code if you stay in Korea for 30 days or longer before flying to China. This is explicitly stated on the Seoul Embassy website.
These transit bans are enforced by each individual embassy so there is no blanket rule.
At least Thailand works as well in this regard (no 30-day rule there), and I assume many other countries.
The ban is intended to prevent people from flying via Canada, Europe, or Japan/Korea, using simple same/next day connections. These flights are often cheap and should be allowed, assuming China actually wants tourists and students to visit again.