There were 57 confirmed cases in China in the 24 hours to midnight on Saturday, the National Health Commission reported.
That was the highest daily toll since mid-April and included 36 in Beijing.
The new cases illustrate how the virus can return as anti-disease controls are relaxed.
The Xinfadi market on Beijing’s southeastern side was closed on Saturday and neighbouring residential compounds locked down after more then 50 people in the capital tested positive – they first confirmed cases in 50 days in the city of 20 million people.
China, where the pandemic began late last year, had relaxed most of its anti-virus controls after the ruling Communist Party declared victory over the disease in March.
Authorities locked down 11 residential communities near the Xinfadi market. Police installed white fencing to seal off a road leading to a cluster of apartment buildings.
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