BEIJING — China began locking down most of its largest city of Shanghai on Monday as a coronavirus outbreak surges and amid questions about the economic toll of the nation’s ‘zero-COVID’ strategy.

China’s financial capital, Shanghai had been relatively unscathed by the pandemic, with lockdowns limited to specific housing compounds and places of work. The citywide lockdown conducted in two phases will be China’s most extensive since the central city of Wuhan, where the virus was first detected in late 2019, confined its 11 million people to their homes at the start of the outbreak in 2020.

Shanghai’s Pudong financial district and nearby areas will be locked down from Monday to Friday as citywide mass testing begins, the local government said. In the second phase of the lockdown, the vast downtown area west of the Huangpu River that divides the city will then start its own five-day lockdown Friday.

Residents will be required to stay home and deliveries will be left at checkpoints to ensure there is no contact with the outside world. Offices and all businesses not considered essential will be closed and public transport suspended.

Already, many communities within the city of 26 million have been locked down for the past week, with their housing compounds blocked off with blue and yellow plastic barriers and residents required to submit to multiple tests for COVID-19.

Shanghai’s Disneyland theme park is among the businesses that closed earlier.

Shanghai detected another 3,500 cases of infection on Sunday, though all but 50 were people who tested positive for the coronavirus but were not showing symptoms of COVID-19. While people who are asymptomatic can still infect others, China categorizes such cases separately from ‘confirmed cases’ – those in people who are sick, leading to much lower totals in daily reports.

Nationwide, 1,219 new confirmed cases of domestic infection were detected on Sunday, more than 1,000 of them in the northeastern province of Jilin, along with 4,996 asymptomatic cases, according the National Health Commission reported on Monday.

China has reported more than 56,000 confirmed cases nationwide this month, with the surge in Jilin accounting for most of them.

China has called its long-standing ‘zero-tolerance’ approach the most economical and effective prevention strategy against COVID-19.

The new measures being enforced in Shanghai aim to “curb the virus spread, protect people’s life and health, and achieve the dynamic zero-COVID target as soon as possible,” the city’s COVID-19 prevention and control office stated in an announcement Sunday evening.

That requires lockdowns and mass testing, with close contacts often being quarantined at home or in a central government facility. The strategy focuses on eradicating community transmission of the virus as quickly as possible.

Although China’s vaccination rate is around 87%, it is considerably lower among older people.

National data released earlier this month showed that over 52 million people aged 60 and older have yet to be vaccinated with any COVID-19 vaccine. Booster rates are also low, with only 56.4% of people between 60-69 having received a booster shot, and 48.4% of people between 70-79 having received one.