Friday, Mar. 4 was an ominous day in the history of the COVID-19 pandemic in China. Health authorities recorded 294 cases, of which 233 were imported. To countries around the world that have made the decision to live with coronavirus and tally daily caseloads in the tens of thousands, these were figures to be envied. But with its zero-COVID policy, China steadfastly refuses to allow the virus to establish a foothold within its borders.

Worryingly, nearly half the imported figure—117 cases—were recorded in China’s most populous province, the southern economic powerhouse of Guangdong. The great majority of those cases, 96, were found in the city of Shenzhen, a booming technology and finance hub that is the jewel of the province. The others were discovered in nearby cities like Zhuhai and Zhongshan—and all but two of the imported cases originated from Hong Kong, where cases have exploded, fueled by the highly contagious Omicron variant. Two days earlier, on Mar. 2, the one-time British colony recorded more than 55,000 cases in a single day and earned the ghastly distinction of being the place with the highest COVID-19 mortality rate in the developed world…

Although only limited movement between Hong Kong and the mainland has been permitted during the pandemic, with significant restrictions on travelers, it is inevitable that Hong Kong’s COVID-19 crisis would spread to the densely populated hinterland, given its proximity. Imported cases from Hong Kong have now been found in at least seven Guangdong cities and provincial authorities are scrambling to contain the damage.