China's commercial capital of Shanghai was dealt a blow on Monday as authorities reported 58 new Covid-19 cases outside areas under lockdown, while Beijing pressed on with testing millions of people on a May Day holiday few were celebrating.

Tough coronavirus measures in Shanghai have stirred rare public anger, with millions of the city's 25 million people stuck indoors for more than a month, some sealed inside fenced off residential compounds, and many struggling to secure daily necessities.

Shanghai residents breathed a sigh of relief at the weekend on news that no cases had been confirmed outside areas under lockdown for two days, but disappointment came on Monday with the report of the 58 new infections.

Authorities did not comment on the new cases at a media briefing but...