The Shenzhen government asked 100 major companies, including iPhone maker Foxconn and oil producer CNOOC Ltd, to implement a "closed loop" system for a week as the southern city battles a COVID-19 outbreak, Bloomberg News reported on Monday.

Foxconn said that operations at its Shenzhen facilities were "normal" and that it would follow government guidelines to ensure safe production.

The city government asked companies including BYD Co, Huawei Technologies Co, and ZTE Corp, to restrict operations only to employees living within a closed loop, with little to no contact with people beyond their plants or offices, the report said, citing a Shenzhen government notice.

The Shenzhen government, Huawei and CNOOC did not immediately respond to request for comment.

BYD, ZTE and Shenzhen-based dronemaker DJI Technology Co declined to comment.

The technology hub of nearly 18 million people reported 21 new locally transmitted COVID-19 infections on Sunday, up from 19 a day earlier, official data showed on Monday.

During an outbreak in March, Shenzhen adopted one week of so-called "slow living", during which residents underwent multiple rounds of testing and largely stayed at home, with one member of each household allowed out every few days to buy necessities.