The sudden spike in COVID-19 infections, particularly imported cases, in the past week more than justifies the SAR government’s enhanced quarantine measures announced on Monday, including banning all non-Hong Kong residents from entering the city effective Wednesday.

That more than 100 new confirmed cases were reported over the past few days, or a staggering 50 percent increase over a week, has led experts to warn that without prompt and decisive action to contain the virus, a large-scale community outbreak is imminent

That more than 100 new confirmed cases were reported over the past few days, or a staggering 50 percent increase over a week, has led experts to warn that without prompt and decisive action to contain the virus, a large-scale community outbreak is imminent, which would not only negate the city’s previous anti-epidemic efforts but also seriously endanger the local economy as well as public health or even the life of many residents.

But the sudden influx of a large number of returnees, mostly Hong Kong students studying in overseas universities, poses another real threat to the city’s quarantine efforts, especially because quite a few of those returnees have not taken the quarantine orders seriously.

Tens of thousands of Hong Kong-born students attending universities in such countries as the United States, the United Kingdom and Australia have recently flown back to Hong Kong after their host countries were more seriously gripped by the potentially lethal novel coronavirus. Most of the returnees are obligated to observe mandatory quarantines at home for 14 days. But dozens of them chose to put other people at risk by going out to have fun at public venues such as stores, restaurants and playgrounds. Some of them went so far as to remove the wristbands put on them by the health authority upon arriving in Hong Kong.

Thanks to the concerted efforts put in by the health authority, medical professionals and ordinary citizens to contain the virus, the city provides those returnees with a safe haven when their host countries are endangered by the virus. But the selfish and irresponsible behavior of some of those returnees could undo all those previous anti-epidemic efforts and put their own hometown in great danger, threatening the health and life of Hong Kong residents, including their loved ones as well as their own.

The police have apprehended five of the 41 known quarantine violators and were searching for the other 36 in the previous 24 hours. These violators should be dealt with according to law and prosecuted without delay to deter such behavior.

Along with imported cases, the number of patients without a travel history during the incubation period also has surged in recent days, suggesting that they were infected locally. The threat of community outbreak remains palpable; Hong Kong residents therefore should continue to strictly observe social distancing and avoid all unnecessary social gatherings. The battle against the novel coronavirus is just half-won; complacency can never be justified.