Authorities will implement mass testing in key neighborhoods deemed to have a relatively higher risk of exposure to COVID-19 over the next two days to curb the spread of the virus, the Shanghai municipal government announced on Wednesday.

Zhao Dandan, deputy director of the Municipal Health Commission, said that the city will not apply the "2+12" measure to these areas. The measure, which refers to two days of home quarantine and 12 days of self-health monitoring, has been implemented before at locations where confirmed or suspected cases have been to.

Shanghai reported 20 new locally transmitted COVID-19 infections on Wednesday, 19 of whom were asymptomatic.

The 19 individuals tested positive during quarantine or were identified during testing of people with potential exposure. One patient was identified during an investigation into individuals arriving in Shanghai from other cities.

Two locations —920 Tingyue Road in Pudong New Area's Huinan town and a dormitory on Jianchuan road in Minhang district — have been listed as medium-risk areas. The Yonghui supermarket on North Huting road in Jiuliting sub-district, Songjiang district, will be downgraded to a low-risk area on Thursday.