The deadly coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, formerly 2019-nCoV), has emerged in Wuhan, China, in December 2019 (WHO, 2020). COVID-19 cases were soon exported to other Chinese cities and overseas, mainly owing to the traffic surge near the Chinese Lunar New Year (Bogoch et al., 2020; Wu et al., 2020). The first imported cases in Hong Kong were confirmed and reported on January 23, 2020, see Fig. 1(a). Since then, the government of Hong Kong has implemented a series of control and prevention measures for COVID-19, including enhanced border screening and traffic restrictions (summary, in press; CHP, in press).