Residents of China's commercial capital of Shanghai scrambled to stock up on groceries as they braced for a lockdown in the city's western areas to stop the spread of Covid-19, while authorities appealed for continued compliance with curbs.

The city, home to 26 million people, is in the fourth day of a two-stage lockdown divided between the historic centre west of the Huangpu River and the financial and industrial district of Pudong in the east.

Public transport in western areas will halt, with residents confined to their homes from 3am on Friday, Reuters reported.

Meanwhile, Shanghai's daily tally of infections eased for the first time in about two weeks, authorities said.