SHANGHAI, March 31 (Xinhua) -- Shanghai will launch a nucleic acid testing campaign in areas west of the Huangpu River starting Friday amid the second phase of the city's closed-off management, an official told a press conference on Thursday.

This round of testing will involve 16 million people, and 12 districts will be put under closed-off management, said Ma Chunlei, secretary-general of the Shanghai municipal people's government.

The megacity with a population of over 24 million on Monday began enforcing temporary closed-off management in two phases to track possible infections and curb the spread of the virus.

Ma said the authorities were making efforts to improve the provision of food supplies as well as address issues with seeking medical help.

The city has converted several venues into temporary isolation centers, and the largest one, located inside the Shanghai New International Expo Center in the Pudong New Area, will start operating soon, local authorities said Thursday.

Covering over 300,000 square meters with over 15,000 beds, the venue will mainly receive patients with mild symptoms and asymptomatic cases.

In collaboration with fresh-food chain Freshippo, Shanghai has dispatched buses to deliver food to residents in communities under closed-off management.

Shanghai reported 355 confirmed locally transmitted COVID-19 cases and 5,298 asymptomatic carriers on Wednesday, said a statement on the website of the Shanghai Municipal Health Commission.