Frozen fish Photo: Xinhua

North China's Tianjin Municipality on Thursday suspended the operations of a local market after finding COVID-19 on its cold-chain products for two consecutive days. 

According to health authorities, a sample collected from a cold storage facility in a wholesale frozen food market in Tianjin's Jinnan district tested positive for the virus.

Operations have been suspended at the market. Four people exposed to the products were quarantined and have so far tested negative for the virus. 

Experts from Tianjin and the National Health Commission have been dispatched to the market to investigate.

On Wednesday, the outer package of imported flatfish sold at a local shop was found to carry the novel coronavirus. The shop's flatfish was bought from the market in Jinnan, media reported. 

Meanwhile, the COVID-19 strain taken from samples in Tianjin shows that the virus belongs to the L genotype of the European branch, sharing a high similarity to the confirmed cases in Beijing's Xinfadi market and Hebei Province from June to July.

Wu Zunyou, the chief epidemiologist at the CDC, told media that customs authorities in many cities across the country found virus-contaminated frozen food imports, presenting growing evidence that frozen seafood or meat may introduce the virus from affected countries into China.

Yang Zhanqiu, deputy director of the pathogen biology department at Wuhan University, told the Global Times that the strong and long duration of the virus in the European branch is critical for the coming winter, and strict control of imported cases from abroad is needed to prevent a second wave in China.

So far, a total of 8,667 close contacts have been investigated in Tianjin, and 808 people are still under medical observation.

As the weather gets colder and the second wave of the global epidemic is fierce, Deputy Foreign Minister Luo Zhaohui said at a Thursday press that China would face a tough winter.

Luo said that as of now, China has reported more than 3,600 imported cases and the number has increased rapidly since October. The current daily average of imported cases is 16.6, up 45 percent from September. 

Defending against imported infections and a domestic epidemic rebound are top priorities for the Chinese government, Luo said, assuring the public that China will continue to deal with the novel coronavirus with an "all-out effort."