A city of 11 million people near China’s capital has been locked down and its residents tested en masse for the coronavirus amid the worst outbreak in about two months in the country, which has largely contained COVID-19 within its own borders.

Authorities in Shijiazhuang banned people and vehicles from leaving the city, located in the province of Hebei that surrounds Beijing, CCTV reported late Thursday. Nucleic acid testing is being rolled out city-wide, and five hospitals have been emptied to treat COVID-19 patients, the state broadcaster said, citing Deputy Mayor Meng Xianghong.

The number of confirmed cases in Hebei rose by 33 on Friday, with 31 of those infections in Shijiazhuang, according to China Daily. That brings the total size of the cluster to 123 confirmed cases, excluding asymptomatic ones, which have also been detected in the mass testing. It’s unclear how the virus took hold in this part of northern China, which had gone about two months without a case before this flare-up emerged.