The United States said Tuesday it had ordered all non-essential employees at its Shanghai consulate to leave, voicing concerns for the safety of Americans in China as the government enforces hard lockdowns to contain Covid-19.

China has stuck to a policy of "zero Covid", aiming to eliminate all infections through rigid shutdowns, mass testing and travel restrictions.

But the policy has come under strain since March, with more than 100,000 cases in Shanghai leading to a lockdown of the city's 25 million inhabitants.

That has sparked widespread outcry over food shortages and an inflexible policy of sending anyone who tests positive to quarantine centres.

The US State Department ordered the departure "due to the ongoing Covid-19 outbreak", a spokesperson from its Beijing embassy said in a statement.

American diplomats have also raised "concerns about the safety and welfare of US citizens with People's Republic of China officials", the statement added. 

"It is best for our employees and their families to be reduced in number and our operations to be scaled down as we deal with the changing circumstances on the ground," it read. 

Shanghai reported more than 23,000 new infections on Tuesday, while dozens of cities across the country battled smaller outbreaks.

Some residents who live in neighbourhoods deemed a low virus risk have been allowed outside their homes this week, but unclear rules have left most in limbo.

One Shanghai resident named Dan said he "couldn't really believe it" when he was permitted to leave his neighbourhood Monday after it was classified a lower-risk area.

But by Tuesday, they had been ordered to stay inside again.

"Several times now there have been promises of lifting the lockdown (that were) retracted at the last minute," the weary American told AFP.

Criticism of China's unrelenting approach to crushing outbreaks is mounting, more so as the rest of the world learns to live with the pandemic.

The European Union Chamber of Commerce has warned that China's coronavirus strategy is "eroding foreign investors' confidence". 

In a letter seen by AFP, it urged Beijing to shift its approach by vaccinating the elderly -- among whom inoculation rates are low -- and allowing people with mild symptoms to quarantine at home.

Analysts at Nomura warned that China has been "facing a rising risk of recession", calculating that 45 cities are currently under full or partial lockdown -- accounting for 40 percent of China's GDP and more than a quarter of its population.

Public anger 

Beijing hit back against the State Department's Shanghai decision on Tuesday, accusing Washington of using the epidemic to "engage in political manipulation".

Shanghai authorities have vowed the city "would not relax in the slightest", preparing tens of thousands of new beds to receive every person who tests positive -- whether or not they show symptoms.

Residents have taken to social media to vent about food shortages and heavy-handed controls, including the killing of a pet corgi by a health worker and a now-softened policy of separating infected children from their virus-free parents.

On Tuesday, Shanghai residents were still deciphering the details of an announcement that allowed some people living in areas with relatively few cases to begin leaving their compounds.

The adjustment on Monday set three levels of controls depending on the caseload.

But freedom still appears far off for most in the city, with at least one southern district set at the lowest level only allowing residents out once a day to buy supplies.

Online discussions on the topic quickly racked up tens of millions of views, with many complaining they were in the lowest tier and still not allowed out.

"The neighbours woke up at six to see if the gate has been opened... (but instead) our completely negative compound has been locked down for another seven days," one wrote in frustration.