Shanghai said on Sunday "unreasonable" curbs on businesses will be removed from June 1 as it looks to lift its Covid-19 lockdown, while Beijing reopened parts of its public transport as well as some malls and other venues as infections stabilised.

China's two largest cities tightened Covid-19 curbs on Monday, fuelling public angst and even questions about the legality of its uncompromising battle with the virus that has battered the world's second largest economy.

The local government in China's capital ordered more Covid-19 tests on Sunday as the city continued to report new local cases, less than two weeks before the start of the Winter Olympic Games.

China's economically important Zhejiang province wrestled on Tuesday with a Covid outbreak that has left half a million people quarantined and some districts under business shutdown.

China could face more than 630,000 Covid-19 infections a day if it dropped its zero-tolerance policies by lifting travel curbs, according to a study by Peking University mathematicians.

Millions of people were confined to their homes in China Monday as the country tried to contain its largest coronavirus outbreak in months with mass testing and travel curbs.

The number of Covid-19 jabs administered in China has passed the one billion mark, health officials said Sunday, more than a third of the doses given worldwide.

A year after his death from Covid-19, residents in the Chinese city of Wuhan say they remain grateful to the "whistleblower" doctor who first sounded the alarm about the outbreak before it received official recognition.

Beijing launched mass Covid-19 testing in some areas on Friday, while Shanghai was testing all hospital staff as China battles its worst outbreak of the disease since March and families fret over reunion plans for the Lunar New Year amid new curbs.

The European Union on Tuesday criticised the jailing of a citizen-journalist in China who reported on the early outbreak of the coronavirus pandemic from Wuhan.

China has tested more than a quarter of a million people for the coronavirus after a handful of new cases were detected in the southern city of Chengdu.

Hundreds of flights at one of China's busiest airports were cancelled Tuesday as Shanghai raced to bring a local coronavirus outbreak under control.