The Chinese Center for Disease Control and Prevention announced it had detected live novel coronavirus on the outer packaging of imported frozen cod in the eastern coastal city of Qingdao, Shandong province, but confirmed that the public was at low risk of infection from touching or eating cold-chain food.

The CDC announced the finding on its website on Saturday.

It is the first time in the world that live novel coronavirus has been isolated from the outer packaging of cold-chain food, the CDC said.

"It has proved that contact with packaging contaminated by the live novel coronavirus could lead to infection. People who work in the frozen cod industry are at high risk," it said. "The new finding is also a reminder for us to pay more attention to the risks from imported frozen food."

The finding was made during an investigation to trace the source of recent infections reported in Qingdao. Between Oct 11 and Tuesday, the city reported a cluster of 12 confirmed coronavirus cases.

The outbreak prompted a campaign to test the city's 11 million residents in five days.

The source of the outbreak has been traced to two dockworkers, according to the local health department. It was spread through poor disinfection of a CT scanning room shared by COVID patients and those with other conditions at a hospital.

The CDC said that the risk of cold-chain food circulating in China being contaminated by the novel coronavirus is very low, citing recent nucleic acid test results for samples taken in the sector.

It said that 2.98 million samples had been tested in 24 provincial-level regions by Sept 15, including 670,000 taken from cold-chain food or food packaging, 1.24 million from workers in the sector and 1.07 million from the environment.

Only 22 samples from cold-chain food or food packaging tested positive for the virus and the viral load on those samples was very low. In addition, the live novel coronavirus had been isolated in the previous tests.

"So far, we haven't found any case among the general public of a person who was infected either from touching or eating cold-chain food. Related departments have intensified surveillance and testing of imported frozen food," said the announcement.

The CDC said daily consumption of cold-chain food is safe but also reminded the public to maintain good health habits, and to handle raw and cooked food separately.

In the announcement, the CDC suggested people who might have close contact with cold-chain food, such as employees in logistics companies, improve prevention methods, avoid skin contact with cold-chain food and regularly take nucleic acid tests.