If rescuing hundreds of passengers from the coronavirus-infected Diamond Princess cruise ship in Japan proved difficult, the operation to bring back thousands of citizens stuck in the epicentre of the outbreak is a monumental task. With the first batch of cruise passengers returned two weeks ago finally out of quarantine, the challenge arising from the Wuhan evacuation has just begun. Few would agree with the claim by Chief Executive Carrie Lam Cheng Yuet-ngor that there was no delay. Many foreign nationals have long been rescued by their governments and finished quarantine back home. But as the saying goes, better late than never. Unprecedented in terms of scale and logistics, the mission is as much a test for the government as for the city as a whole. Some 500 Hongkongers are expected to take the four chartered flights arranged by the government today and yesterday . Efforts to bring back the remaining 3,200 citizens stranded across the hardest hit province of Hubei will continue. In one extreme case, it would take seven hours by car for a stranded person to reach the airport. But how to gather everyone for efficient evacuation is one thing, the health risk is another. With thousands returning from the infections zone, the threat to public health must not be ignored. About 100 Hongkongers from cruise ship to be out of quarantine on Thursday Given the Wuhan outbreak has yet to come under control, the operation is a risky affair. Officials appear to be highly vigilant, as shown in images posted on social media by constitutional and mainland affairs chief Patrick Nip Tak-kuen, the minister in charge of the exercise. Credit also goes to immigration and medical officers taking part, especially those who joined the cruise ship evacuation as well. Their experience will help ensure a smooth operation. Concerns have been raised about the lack of quarantine measures for officials returning from Wuhan. Even if they wear full protective gear and do not venture beyond the airport, it is wise to err on the side of caution. For their own interest as well as that of the department concerned and the wider community, they should avoid contact with others upon return to keep the risk of infection to a minimum. Having been stranded for so long in the epicentre, the returnees must also strictly observe quarantine rules. If the Diamond Princess experience is any reference, some passengers who tested negative before boarding their chartered flights eventually came down with the disease upon return. It would not be surprising if the same happens to those returning from the mainland. That makes stringent quarantine all the more important. The good news is that more people in the public housing-turned isolation camps are leaving after completing the procedure. With good planning and cooperation, the crisis can be defused.