There are now 216 areas designated as high or medium risk in mainland China, the highest number since the epidemic control became “normalised” last year.

Nanjing, with a population of 9 million, has finished five rounds of mass testing and is conducting the sixth round of partial regional testing, while new rounds of mass testing are continuing in other cities hit by outbreaks.

The NHC on Sunday ordered officials across China to make halting the spread of the virus their top priority as cases soared. It also asked health officials to keep a tight grip on hospital infection prevention and control.

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In Zhoushan in eastern Zhejiang province, authorities said a rescue was under way after a Chinese sailor posted a video on social media calling for help on Sunday. The sailor, Guo Yuqiang, said 13 crewmates from the cargo ship Grand Progress, which had returned from the Philippines after delivering coal, had feverish symptoms but could not get medical treatment because the ship had been refused permission to dock by Nantong, a port city in Jiangsu.

The Zhoushan government said in a statement the ship was refused permission to dock by the destination port and was stranded in Zhoushan waters, and an emergency rescue operation was under way.

All 38 new confirmed infections in Jiangsu province were in the city of Yangzhou, up from 36 a day earlier. No new cases were reported in Nanjing, the early epicentre of the latest round of outbreaks.

Yangzhou had so far reported a total of 346 confirmed local cases, including six who are in critical condition, Wang Jinsong, deputy head of the Yangzhou Health Commission, said on Monday morning.

There are two high-risk areas and 83 medium-risk areas in the city, which has launched its fifth round of mass testing.

The Communist Party’s disciplinary watchdog for Yangzhou said on Sunday that faults with the operation of a testing site in Guangling district had caused infections to spread to a number of people who came for tests on July 29, as they came into close contact with a government staff member who was confirmed as a Covid-19 case on August 1.

The staff member has been investigated and suspended for serious violations. A dozen local leaders and officials were also reprimanded and punished.

As of Saturday, 25 cases had been traced to the testing site, including three testing staff and 22 residents who were sampled, Shanghai-based media outlet The Paper reported.

All inbound and outbound rail connections to Yangzhou were halted on Friday in view of the serious virus resurgence there.

Jiangsu has suspended the operation of mahjong pavilions and chess rooms across the province. The southern Chinese cities of Guangzhou and Shenzhen, the northeastern city of Shenyang, and others have also issued similar orders.