China's commercial hub of Shanghai has ground to a halt after the government locked down most of the city's 26 million residents to stop the spread of Covid-19, even as official numbers put local cases falling for the second day in a row.

The city government extended an existing lockdown in eastern districts, just as western parts of the city were shut down as scheduled, Reuters reported.

Fresh official guidance indicated that many in China's most populous city will now be required to stay home as long as it takes to control the outbreak — instructed not to cross their doorsteps even to dispose of rubbish or walk their dogs.

Public transport in most of the city has been suspended, while businesses considered non-essential, like restaurants and shopping malls, have also had to close.