Deputy Mayor Zong Ming praised the support from the public and the work of frontline workers despite public criticism of strict curbs, but said the handling of the virus needed to improve.

"We feel the same way about the problems everyone has raised and voiced," Zong told a daily briefing on Saturday.

"A lot of our work has not been enough, and there's still a big gap from everyone's expectations. We will do our best to improve."

Beijing intervened after the failure of Shanghai's initial effort to isolate the virus by locking down in stages, insisting the country stick to its zero-tolerance policy to prevent its medical system being overwhelmed.

Elsewhere on Saturday, the southern megacity of Guangzhou - home to more than 18 million people - said it would begin testing in all 11 of its districts after cases were reported there on Friday.

In Beijing, the municipal government placed a high-risk area under lockdown after eight confirmed COVID cases in the past two weeks, the Beijing Center for Disease Prevention and Control said.

In Shanghai, where 26 million people are in lockdown, residents have continued to complain about food shortages due to a lack of couriers and uncertainty about when lockdown curbs may end.

The government said it would conduct more testing on Saturday and would ease some movement curbs. It did not signal a change of approach, however.

"The epidemic prevention and control is now at the most critical moment, and we cannot tolerate the slightest slack," Zong said.

Gu Jun, director of the city's commerce commission, acknowledged problems in distributing food supplies and said distribution centres, supermarkets, and pharmacies should continue operating online as much as possible.

Australian Associated Press