The Chinese Center for Disease Control and Prevention (CDC) made the conclusion after it detected and isolated living coronavirus on the outer packaging of frozen cod.

The CDC was trying to trace the virus in an outbreak reported last week in the city of Qingdao, the agency said on its website.

The finding, a world first, suggests it is possible for the virus to be conveyed over long distances via frozen goods, the CDC said.

Two dock workers in Qingdao who were initially diagnosed as asymptomatic infections in September brought the virus to a chest hospital during quarantine due to insufficient disinfection and protection, authorities said last week.

It led to another 12 infections linked to the hospital.

However, the CDC's latest statement does not show solid proof that the two workers in Qingdao caught the virus from the food packaging directly, University of Hong Kong virology professor Jin Dong-Yan said.

It's possible they contracted the virus from somewhere else and then contaminating the food packaging they handled, he said.

The CDC said no instance had been found of any consumer contracting the virus by having contact with frozen food and the risk of this happening remained very low.

Nonetheless it advised workers who handle, process and sell frozen products to avoid direct skin contact with products that could possibly be polluted.

Staff should not touch their mouth or nose before taking off work garments that could possibly be contaminated without washing their hands and should take tests regularly, the agency said.

Prior to the CDC's latest findings, genetic traces of the virus had been found in some samples taken from frozen food or food packaging.

However the agency said the amount of virus was low and no living virus was isolated.

Only living virus can infect people, while samples containing dead virus can also test positive for virus traces.

Australian Associated Press