SHANGHAI: China's commercial hub of Shanghai faces an unexpected round of mass COVID-19 testing for most residents this weekend - just 10 days after a city-wide lockdown was lifted - unsettling residents and raising concerns about the impact on business.

Shanghai officials on Thursday said seven of the city's 16 districts would carry out PCR testing for all residents over the weekend due to the discovery of a few cases in the community, saying they wanted to prevent a renewed outbreak. 

Another six districts announced similar plans later in the day. Some of the districts said residents would not be allowed to leave their homes while the testing was carried out.

"During the sampling communities will carry out 'closed management', there will be only entry and not exit, which will be lifted after the sampling is over," read one notice from Changning district.

"We hope that residents ... will participate in an orderly way in the PCR testing."

The announcements were greeted with surprise and concern, with some taking to the Twitter-like Weibo platform to ask how the testing would affect plans for the weekend, such as moving house or seeing a doctor. Many expressed fear they could be locked down again.

The move comes on top of already onerous testing requirements that the city introduced for its 25 million residents after easing a city-wide lockdown on June 1.

Residents need to have proof they have taken a COVID test within the last 72 hours to enter areas like malls and offices - or even to use subways and buses. Many have become frustrated about having to queue in hours-long lines at more than 15,000 booths scattered around the city to do so. 

Some parts of the city have remained under or returned to lockdown shortly after June 1 due to positive cases and their close contacts. Three of the latest infections that have led to several closures were traced to a popular beauty salon in the city centre that reopened when the city did on June 1.

While China's infection rate is low by global standards, President Xi Jinping has doubled down on a zero-COVID policy that authorities say is needed to protect the elderly and the country's medical system, even as other countries try to live with the coronavirus.

Shanghai's two-month lockdown fuelled widespread frustration, anger and even rare protests among its residents, as they grappled with lost incomes, the loss of freedom, the death of friends and relatives, and even hunger.

It also battered the Chinese economy, disrupted supply chains and slowed international trade.