The numbers are small, but the major port of Tianjin may be facing China's first outbreak of Omicron of any size, less than four weeks before the Winter Olympics open in nearby Beijing.
The city began mass testing of its 14 million residents on Sunday after a cluster of 20 children and adults tested positive for Covid-19, including at least two with the Omicron variant. Officials said the virus has been circulating so the number of cases could grow.
China has stepped up its strict zero tolerance strategy in the run-up to the Olympics, which open Feb. 4. The Chinese capital is 115km northwest of Tianjin and many people regularly travel back and forth by car or on a high-speed rail link that takes less than one hour.