Hong Kong raised its response level to "serious", from "alert" on its three-level system. The third is "emergency".
The "serious" level means tighter controls at points of entry to Hong Kong, greater coordination between authorities and swifter test results for suspected cases.
"The Department of Health advises the public to avoid unnecessary travel to Korea, in particular, those with chronic illnesses," Hong Kong's Centre for Health Protection said.
"Travellers in Korea and the Middle-East should avoid unnecessary visit to healthcare facilities."