Containers to be loaded on vessels for export at Qingdao Port in East China's Shandong Province File Photo: IC

Two workers who offloaded imported seafood at Qingdao port in East China's Shandong Province have tested positive for the coronavirus and both are asymptomatic, local health authority said on Thursday. 

As of press time, a total of 147 close contacts of the two workers have been quarantined and are under observation, all have tested negative for the coronavirus. 

Another 4,341 people have also tested negative during local community screening. 

Authorities have tested 1,440 samples from the products and the warehouse, of which 51 have shown a positive result. The products have been sealed off and have not been sold to consumers. 

A 40-year-old worker surnamed Dong offloaded imported frozen seafood on Saturday and he tested positive on Thursday although he had no symptoms. Another worker surnamed Chen also loaded imported seafood on Saturday and he was tested positive for COVID-19 infection.  

From July to mid-August, 10 positive coronavirus cases were reported in nine locations on the imported frozen seafood or the packaging. Seven involve frozen white shrimp from South America, according to media reports. 

And some experts believe that the virus can remain active longer in cold chain transportation and can even survive for years at temperatures of minus 10 to 30 degrees Celsius.

Four days ago, samples taken from packaging of imported squid tested positive for coronavirus in Changchun, Northeast China's Jilin Province, local health authority said on Sunday.