Shanghai reported 61 new locally transmitted COVID-19 infections on Sunday, of which 55 were asymptomatic, the municipal government said at a news briefing.

Two of the confirmed cases were previously reported asymptomatic and already under medical quarantine at a designated hospital, and the other four were close contacts of previous confirmed cases who were under hotel quarantine.

Among the asymptomatic infections, 44 were found during hotel quarantine as they were close contacts of previous cases or infections, and the rest were discovered when conducting nucleic acid tests among people with risk of exposure to the virus.

As of 5 pm Sunday, altogether 8,985 close contacts and 27,548 secondary close contacts involved in the current local outbreak since March 1 have been identified and subject to quarantine measures.

In addition, residents in many neighborhoods have participated in mass nucleic acid testing.

"Such measures are taken because there is hidden spread of the virus outside of transmission chains already identified by disease control workers, and we need to race against time to find them," said Wu Fan, a core member of Shanghai's expert epidemic control team and vice-dean of Fudan University Shanghai Medical College.

"Some other measures announced by the city government since Friday, including requiring residents to avoid unnecessary trips out of the city and school suspension starting Monday, are meant to reduce people's social activities and gathering so as to achieve the goal of zero infections out of the transmission chains as soon as possible," she said.

Liu Min, vice-director of the Shanghai Municipal Commerce Commission, said it has confirmed with multiple supermarkets and online shopping platforms to jointly provide necessary supplies to residents, especially those in neighborhoods under closed-loop management.

"There is no need for residents of the city to purchase excessively at the moment. The market supply is more than sufficient," she said.