A senior official from Qingdao, Shandong province, vowed to improve cold-chain food management further after one of two asymptomatic coronavirus infections reported on Tuesday was directly linked to imported frozen food.

Chen Wansheng, deputy director of the general office of the city government, said in a news conference on Wednesday that Qingdao had spared no effort to prevent the spread of coronavirus via imported cold-chain food. It has built special warehouses to collect and examine imported frozen food.

"Qingdao is one of key port cities of cold-chain food imports and exports. All imported aquatic products and meats entering the city from overseas and those supposed to be sold directly in the city's markets are required to be disinfected and receive nucleic acid tests," said Chen, adding that only some eligible products can be certified outside the warehouse and be allowed for market circulation.

"Four more special warehouses are expected to be added," Chen added.

As of Monday, the city had carried out disinfection procedures on a total of 3,513 metric tons of imported cold-chain food, it was noted at the news conference.

At the same time, the city is also tightening the health management of staff members who are engaged in tasks involving cold-chain food.

As of 9 am on Wednesday, the city had tested a total 48,435 cold-chain workers. So far, 48,315 results have returned, all of them negative.

The local health authority reported two asymptomatic coronavirus cases on Tuesday.

One of those was a 30-year-old man surnamed Li who handled imported cold chain products. He is currently living in Jiaozhou, a county-level city of Qingdao, and has been working at a company dealing with aquatics products. He is responsible for handling goods, and for disinfection.

The other case is the man's 33-year-old sister, who lives with him in the same apartment. Her nucleic acid test was positive as the local health authority was tracing her brother's contacts. Both are now in a designated hospital for observation.

Local health authorities have traced and tested 594 contacts of the man and woman, as well as 281 contacts of those contacts, 187 general contacts and another 603 people. So far, all tests have come back negative.