STORY: Shanghai will lock down millions of people again over the weekend, just 10 days after lifting its gruelling two-month confinement.
Authorities have ordered PCR testing for all residents in 14 of the city's 16 districts.
Five of the districts said residents would not be allowed to leave their homes while the testing was carried out.
The Chinese commercial hub is racing to stop a wider outbreak after discovering a handful of community cases.
The latest scare triggered another rush to grocery stores and online platforms to stock up on food.
Some areas had remained sealed off or quickly returned to lockdown due to infections and their close contacts.
Zhang Jian is a 34-year-old estate agent:
"Of course I am worried, lockdown was just lifted on June 1. We are slowly recovering and returning to some semblance of normal work. The residential compound next to mine has already been under lockdown. If there is a mass testing and there is another positive case in the compound, it will have a serious impact on our lives, including our work."
The latest round of mass testing comes on top of already heavy testing requirements in Shanghai after easing its earlier lockdown.
Residents must prove they have been tested within the last 72 hours to enter areas like malls and offices or even to use subways and buses.
The city's earlier lockdown fuelled widespread frustration, anger and even rare protests among its residents.
Many grappled with lost income, the loss of freedom, the death of friends and family, and even hunger.
Meanwhile, in Beijing, authorities shut entertainment and internet venues in two of the capital's largest districts after tracing cases to a few bars.