BEIJING (BLOOMBERG) - The latest Covid-19 resurgence in China is putting imports of frozen food back under intense scrutiny as the authorities act on a controversial claim that it is possible to contract the virus from food packaging.

Cities including Zhengzhou and Haikou will tighten inspection of imported frozen food to prevent virus transmission, according to local media reports.

Frozen pork bone and beef ribs originating from Britain, Brazil and Canada were seized from a hot pot restaurant in Nantong city as the operators could not provide disinfection certificates or nucleic acid test reports.

China has claimed that the virus can persist in conditions found on frozen food and packaging, linking some infections in people to imported goods, and has taken drastic steps to curb the risk.

The international health authorities have downplayed the likelihood of such transmission, with the World Health Organisation and the United States Centres for Disease Control and Prevention saying that the chance of getting Covid-19 from frozen foods is very low.

Despite this, China has been testing cold food shipments for virus traces for months; some supermarkets even have separate coolers for imported goods.

It is a debate with global ramifications because China is one of the world's biggest buyers of many food products, accounting for almost half of the global pork trade.

Earlier this year, the mass testing and disinfection of frozen food caused severe port congestion and long customs clearance delays.

The latest outbreak, which was first detected at Nanjing airport in late July, is linked to the highly infectious Delta variant and has spread to nearly half of China's 32 provinces within just two weeks.

Nanjing has investigated more than 13,000 cold chain food production and business units since the outbreak and tested more than 35,000 samples, all of which were negative for the virus.