Authorities in the Chinese city of Wuhan will begin testing its entire population after a handful of positive cases of coronavirus have been detected there.
Wuhan has recorded seven cases of local transmission, the first local infections in more than a year.
The city of 11 million people jumped into the limelight after the coronavirus was first detected there in 2019.
China is currently experiencing one of its biggest outbreaks in months, with 300 cases detected in 10 days.
Some 15 provinces across the country have been affected, prompting the government to deploy mass testing measures and shutdown restrictions.
Authorities have attributed the spread of the virus to the highly contagious Delta variant and the domestic tourism season.
The announcement in Wuhan came as China reported 90 new cases of the virus on Tuesday.
The National Health Commission said 61 of them were locally transmitted, up from 55 local cases the day before.
China had largely managed to control the virus within its borders.
However, this new spread, first detected among workers at a busy Nanjing airport, has sparked concern.
Authorities have tested Nanjing’s 9.2 million residents three times and imposed a lockdown on hundreds of thousands of people.
But over the weekend the focus of attention turned to the popular tourist destination of Zhangjiajie in Hunan province, where many of the latest cases have emerged. Travelers from Nanjing are believed to have visited the city recently.
Health authorities have focused on a theater in Zhangjiajie, and are now trying to track down some 5,000 people who attended performances and then traveled back to their hometowns.
“Zhangjiajie has now become the new ground zero for the spread of the epidemic in China,” Zhong Nanshan, China’s leading respiratory disease expert, told reporters.
The new outbreak has also reached the capital, Beijing, where several locally transmitted infections have been reported.