Authorities in Wuhan on Tuesday said they would test its entire population for Covid-19 after the central Chinese city where the coronavirus emerged reported its first local infections in more than a year.
The city of 11 million is "swiftly launching comprehensive nucleic acid testing of all residents", senior Wuhan official Li Tao said at a press conference on Tuesday.
Authorities announced on Monday that seven locally transmitted infections had been found among migrant workers in the city, breaking a year-long streak without domestic cases after it squashed an initial outbreak with an unprecedented lockdown in early 2020.
China has confined the residents of entire cities to their homes, cut domestic transport links and rolled out mass testing in recent days as it battles its largest coronavirus outbreak in months.
China reported 61 domestic cases on Tuesday as an outbreak of the fast-spreading Delta variant reached dozens of cities after infections among airport cleaners in Nanjing sparked a chain of cases that have been reported across the country.
Major cities including Beijing have now tested millions of residents while cordoning off residential compounds and placing close contacts under quarantine.
The eastern city of Yangzhou, near Nanjing, was the latest local government to order residents to stay home after large-scale testing detected 40 new infections over the past day.
The more than 1.3 million residents of Yangzhou's urban core are now confined to their homes, with each household allowed to send only one person outside per day to shop for necessities, the city government said Tuesday.
The announcement comes after the tourist destination of Zhangjiajie in central China's Hunan province as well as nearby Zhuzhou city issued similar orders in recent days to more than two million people combined.
The outbreak spread to Hunan from Nanjing last month after people infected at the Nanjing airport cluster attended theatre performances in Zhangjiajie.
Officials have since been desperately tracking down thousands of fellow theatregoers and urging tourists not to travel to areas where cases have been found.
Meanwhile, Beijing has blocked tourists from entering the capital during the peak summer holiday travel season and asked residents not to leave unless necessary, with top officials vowing over the weekend to "spare no expense" in defending the city.
China had previously boasted of its success in bringing domestic cases down to virtually zero after the coronavirus first emerged in Wuhan, allowing the economy to rebound.
But the latest outbreak is threatening that success with more than 400 domestic cases reported since mid-July.