SHANGHAI (BLOOMBERG) - Shanghai's 25 million residents are almost all under some form of lockdown as the financial hub scrambles to tame a relentless surge of the coronavirus's highly contagious Omicron variant.

The eastern half of the mega Chinese city remains under tight movement restrictions despite the end of a four-day sweeping lockdown on Friday (April 1) morning, according to a government statement on Saturday.

That means the entire population of the metropolis is currently under some form of quarantine as the two-part lockdown shifted to the western half of Shanghai on Friday.

Residents in the western part of the city, where about two-thirds of its population live, began their four-day lockdown at 3am local time on Friday after the programme ended in the east.

During the restrictions, residents are barred from leaving home unless they are going out for mandatory mass Covid-19 tests.

Shanghai has emerged as the epicentre of China's worst virus outbreak since the early days of the pandemic. The city's daily infections shot up from less than five at the beginning of March to more than 6,300 on Friday, official data show on Saturday.

The spread of the highly transmissible Omicron strain to Shanghai - home to the world's largest container port and country headquarters of many domestic and overseas companies - is the biggest test yet for President Xi Jinping's dual goals of eliminating the virus while minimising the economic and social impacts of a Covid-zero strategy.

While the lockdown of Shanghai's east officially ended at 5am local time on Friday, not all residents will be able to leave their homes immediately under a what the local government described as a tiered quarantine regime.

The rules require anyone living in a building where a Covid-19 case has been reported to stay confined in their home for two weeks. Residents of other buildings in the same compound as the block where a positive patient was reported will be subject to seven-day home quarantine.

Residents living close to locked-down compounds will be confined to their neighbourhood for a week, and limited to sending one person from each household out once a day to fetch necessities delivered to them.

As of Saturday, all of the almost 9 million residents of the eastern half of the city were still subject to some form of restrictions, according to the official statement. Nearly 40 per cent of Saturday's newly reported infections in the city came from the eastern part, known as Pudong.

The worsening outbreak in Shanghai is further weighing on the world's second-largest economy and threatening to disrupt global supply chains.