Two weeks ago, it seemed that Hong Kong had successfully contained the deadly coronavirus sweeping the world. The daily number of new cases in the city was steady and relatively low. There was cautious optimism that control measures adopted at an early stage had succeeded. But with the virus spreading rapidly in Europe, the United States and elsewhere, it was clear the danger had not passed. Now, as the number of imported cases grows, the risk of a widespread community outbreak is greater than at any time in the past two months. Every effort must be made to stop the transmission of the virus and to limit the number of cases of the Covid-19 disease. Over the past two weeks, around 80-90 per cent of new cases in Hong Kong are either people with a travel history or close contacts of those who have travelled. Thousands hurried back to the city from overseas, seeing it as a safe haven. The overwhelming majority of those returning are Hong Kong residents. Since Thursday, all arrivals must stay isolated at home and are subject to checks. They must wear a wristband that alerts the authorities if they stray. But the government has, so far, resisted calls to impose a ban on all arrivals except residents. This is a drastic step to take, especially for an international city such as Hong Kong. But the priority must be to win the war against the virus and to protect public health. Governments around the world are imposing tighter travel restrictions. Singapore has barred short-term visitors from entering or transiting the city amid concerns they would head there for tests or superior medical care. With entry to Singapore barred, Hong Kong becomes an even more appealing destination. It is time for the government to impose a similar ban. An exception could be made for those with special reasons to visit. A ban is needed to reduce the risk of imported cases. Further measures may be required. Chief Executive Carrie Lam Cheng Yuet-ngor announced on Saturday that university entrance exams would be postponed, public facilities closed and that civil servants must resume working from home. She also called on people not to visit bars and restaurants, but has not gone so far as to order such venues to close. A community effort is needed. Recent arrivals from overseas, including those who beat the quarantine deadline, should self-isolate for two weeks. Anyone breaching quarantine rules must be punished. The best advice at this critical time is for people to stay at home and to limit human-to-human contact. Hong Kong has kept the virus at bay largely because the community took it seriously and quickly adopted preventive measures. It is a fast-moving situation. But if the government acts decisively and people remain vigilant, the virus can still be contained. Purchase the China AI Report 2020 brought to you by SCMP Research and enjoy a 20% discount (original price US$400). This 60-page all new intelligence report gives you first-hand insights and analysis into the latest industry developments and intelligence about China AI. Get exclusive access to our webinars for continuous learning, and interact with China AI executives in live Q&A. Offer valid until 31 March 2020.