Shanghai will ensure the efficient operation of domestic and international transport amid its new round of COVID-19 mass testing, during which the city will be locked down over two phases starting on Monday, the municipal government said at a briefing held on Monday.

Authorities stressed that airports, railways, international passenger and cargo services will be operating as per normal.

"Although we have strict control measures, our airports, railways and international passenger and cargo services are operating normally," said Wu Jinglei, director of the Shanghai Health Commission, at Monday's press briefing.

Under the new testing strategy announced on Sunday, regions east of the Huangpu River will be locked down from Monday till 5 am on Friday for COVID-19 testing. The rules will apply to regions west of the river from 3 am on Friday to 3 am on April 5.

Enterprises in locked down regions must enforce closed-loop management and allow employees to work from home. Buses, subways, ferries, taxis, and online car-hailing services will be suspended during the lockdown.

On Sunday, the city reported 3,500 new locally transmitted COVID-19 infections, 50 of which are confirmed cases. Two areas were downgraded to low risk - 9 Jumenhou road, Dapuqiao sub-district in Huangpu district, and 760 Loutang road, Jiading Industrial Zone, Jiading district.

"The grid screening the city carried out over the past two weeks has revealed that the virus has spread in clusters across the city and there is a risk of further outbreaks. It's necessary to implement stricter measures now," said Wu Fan, a member of the expert team leading the Shanghai COVID-19 prevention and control efforts at the briefing.

"The new round of testing aims to reduce social mobility, identify infections, and eliminate the transmission of the virus in neighborhoods so as to protect people's lives and achieve zero spread outside virus transmission chains as soon as possible," she added.