Covid cases in Shanghai hit their highest level yet as authorities in the locked-down city stepped up their battle to suppress China’s worst outbreak in two years.

Shanghai, which is sealed off from the rest of the country as part of the most severe citywide measures since the virus emerged in Wuhan, reported 24,952 new cases on Sunday.

The protracted lockdown of Shanghai, China’s largest city and its leading financial hub, is the biggest test yet of Xi Jinping’s zero-Covid policy, which aims to eliminate the virus through restrictions on movement, mass testing and centralized quarantine of patients.

Sunday’s figures, which refer to cases from the previous day, came after authorities in the city announced a new round of mass testing at a time when most of its 26mn residents remain confined to their homes with an uncertain release date. Complaints over access to food have circulated widely on social media.

Zong Ming, deputy mayor of Shanghai, said lockdowns of communities would be lifted if they reported no positive cases for 14 days.

After weeks of locking down individual buildings, the city began a two-stage lockdown on March 28. Initially supposed to last for four days in each half of the city, it has since been extended.