Shanghai will lock down a district in the south west on Saturday morning to conduct a mass COVID-19 testing drive, its first major movement restriction since the financial hub exited a bruising two-month shutdown at the start of June.

The mini-lockdown is raising concerns that the city’s reopening is backsliding as officials fear a rebound in cases. While the plan is to seal the Minhang district of 2.65 million people only for the morning, residents face the risk of being confined to their homes for another two weeks if any COVID-19 infections are discovered, in line with China’s "COVID zero" policy.

Elsewhere in the city of 25 million, officials appear to be escalating curbs and placing apartment blocks back under lockdown over the slightest hint of infection risk. Some housing compounds in the central Jing’an and Xuhui districts were sealed for 14 days from Tuesday, although only close contacts — no confirmed cases — were found among residents.

The threat of renewed restrictions is looming over all of Shanghai as the city slowly emerges from the lockdown implemented in late March. While most residents have regained their freedom since the start of the June, hundreds of thousands are grappling with varying limitations and the abrupt imposition of new curbs. The constant risk of resurgence and the measures needed to prevent them underscores the stress stemming from the zero-tolerance strategy still followed in the world’s most populous country.

Nationwide, China reported 164 infections for Wednesday, including nine in Shanghai. Most of the country’s cases were in Inner Mongolia, in China’s north, where the number rose to 130 from 81 the previous day and some areas remain locked down. In the capital of Beijing, just one new infection was recorded.

Besides the lockdowns, mass testing is being rolled out at numerous housing compounds around Shanghai, which can surface infections that will lead to wholesale curbs again.

In the city’s Xuhui and Jing’an districts, people in some affected areas are barred from leaving their homes and are subject to a daily COVID-19 test, according to the latest policy. Others will be quarantined for seven days, followed by another week of health monitoring at home. During the control period, all vehicles in regions except for buses and ambulance are banned, according to government statements.