BEIJING (AP) — 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.