The Ministry of Health reported nearly 300 new positive Covid-19 cases nationwide on Wednesday.
The main affected area is the eastern province of Anhui, where 1.7 million people in two rural townships are currently confined.
But since Sunday positive cases have also been observed in Shanghai.
Mandatory drug tests were launched in most districts, while all karaoke bars in the city were closed on Wednesday.
Some infections appear to be linked to these entertainment venues, authorities say.
Some Shanghai residents fear a return to restrictions, five weeks after the lifting of a two-month lockdown in China's largest city.
A concern amplified by the reception by some households of food rations, according to messages widely shared on social networks.
"The Putuo district (in central Shanghai, editor's note) is sending vegetables again," wrote a resident on WeChat messaging.
Some 1,400 km away, the large city of Xi'an (north) for its part reimposes "control measures", after an outbreak of Omicron linked to the BA.5.2 sub-lineage, according to local health authorities.
This strain is reputed to be more contagious but less virulent.
It nevertheless constitutes a new challenge for China, one of the last countries to apply a so-called “zero Covid” strategy in the face of the epidemic.
This health policy consists of massive screenings, mandatory quarantines in the event of a positive PCR test and targeted confinements.
The government considers this method necessary to save medical resources and preserve the elderly, whose vaccination rate is relatively low.
But it is dealing a severe blow to economic activity with many businesses closed or operating at idle.
According to estimates by Nomura Bank, at least 114 million Chinese are currently subject to various travel restrictions, including confinements.
They were 66 million just a week ago.
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