A medical worker in full protective gear collects a sample from frozen food packaging Monday in a cold storage warehouse in North China’s Tianjin municipality.

A medical worker registers the personal information of a man who is taking a nucleic acid test.

Medical workers prepare to carry out tests on frozen food in a Tianjin warehouse.

A medical worker prepares to take a frozen chicken from a packing box.

A warehouse worker takes a nucleic acid test.

Warehouse workers line up to take nucleic acid tests. Tianjin concluded testing of more than 77,000 residents for Covid-19 in the Binhai New Area Wednesday morning, all of whom tested negative.