A health worker wearing personal protective equipment (PPE) talks to residents of a small residential building during a Covid-19 coronavirus lockdown in the Jing'an district of Shanghai on April 16, 2022. Hector RETAMAL / AFP

City authorities revealed the first deaths of this outbreak on Monday, with Tuesday's fatalities bringing the official toll to just 10, even as the virus continues to spread.

Beijing insists its zero-Covid policy of hard lockdowns, mass testing and lengthy quarantines has averted fatalities and the public health crises that have engulfed much of the rest of the world.

But some have cast doubt on official figures in a nation where the vast elderly population has a low vaccination rate.

By comparison, Hong Kong -- which also has a high number of unvaccinated elderly -- has tallied nearly 9,000 deaths among 1.18 million Covid-19 cases since the Omicron variant surged there in January.

Unverified social media posts have claimed Shanghai's deaths are going unreported, but the messages have been quickly scrubbed from the internet.

Shanghai health officials said Sunday that less than two-thirds of residents over 60 had received two Covid jabs and under 40 percent had received a booster.

The seven newly reported deaths were all unvaccinated patients, city health official Wu Qianyu told a press conference on Tuesday.

They were aged between 60 and 101, and suffered from underlying conditions such as heart disease and diabetes, according to the Shanghai Municipal Health Commission.

The patients "became severely ill after admission to hospital, and died after ineffective rescue efforts, with the direct cause of death being underlying diseases", the commission said.

Shanghai logged more than 20,000 new and mostly asymptomatic Covid cases Tuesday, defying officials' efforts to stamp out the infection.

Many of the city's 25 million residents have been confined to their homes since March, with some flooding social media with complaints of food shortages, spartan quarantine conditions and heavy-handed enforcement.

Protest footage has circulated faster than government censors can delete it.

The country's zero-tolerance approach to Covid had largely slowed new cases to a trickle after the virus first emerged in the central Chinese city of Wuhan in late 2019.

But officials have scrambled in recent weeks to contain an outbreak spanning multiple regions, largely driven by the fast-spreading Omicron variant.

By one estimate on Monday, around 350 million people in at least 44 cities are currently under some form of lockdown in China.