Hong Kong will put all visitors under a two-week quarantine and medical surveillance starting midnight on March 19 to prevent further spread of the new coronavirus, chief executive Carrie Lam said at a press briefing.
The government also told Hong Kong residents to avoid all non-essential travel and issued its second-highest red outbound travel alert to all countries and territories except for mainland China, Macao and Taiwan.
As of Monday, Hong Kong, which is one of Asia's major financial hubs, has confirmed 157 cases and four deaths in the city. The first cases in the city were detected as early as January but swift measures, as well as social distancing efforts, kept the number of infections relatively low.
The coronavirus, which was first detected in China's Hubei province, causes the COVID-19 disease that infected at least 168,000 people worldwide and killed more than 6,600 people, according to data from the World Health Organization. Many countries have recently stepped up travel restrictions and business closures to prevent the virus from spreading.
Lam said Hong Kong recorded 57 new cases in recent weeks, and 50 of those cases are imported from overseas and that local transmission remained low. Without taking stringent measures at the moment, Hong Kong's past efforts to prevent the spread of the disease would go to waste, she said in a translation of her remarks.
Lack of proper measures could lead to community outbreaks and burden Hong Kong's health care system.
Separately, the gambling destination of Macao will block entry by anyone except people from mainland China, Hong Kong or Taiwan.
The ban, announced Tuesday by the Macao government's Novel Coronavirus Response and Coordination Centre, goes into effect at midnight local time on March 18.
—CNBC's Ted Kemp, Vivan Kam and Yolande Chee contributed to this report.