QINGDAO, Sept. 25 (Xinhua) -- Two stevedores in east China's port city of Qingdao were reported as asymptomatic COVID-19 cases on Thursday, said the municipal health commission on Friday.

The two workers, aged 40 and 45, respectively, had both handled imported frozen seafood on Sept. 19. Nucleic acid tests revealed the two were positive for novel coronavirus on Thursday.

So far, 147 close contacts of the two, together with another 228 who had close contact with those 147 people, have been placed under quarantine. They have all tested negative for COVID-19.

Meanwhile, all 4,341 people who either had casual contact with the two or live in the same neighborhoods with them also had negative nucleic acid test results.

The municipal health commission said the batch of imported products had not yet entered the market and has been sealed.

A total of 1,440 samples taken from the cold chain products and the surrounding environment have been collected and tested, and 51 samples have tested positive, said the commission.