The number of flu outbreaks almost tripled in the last two weeks of February, with 112 recorded nationwide in the week ending February 19, according to data from the China National Influenza Centre. In China, outbreaks involving at least 10 people must be reported to health authorities.

Nearly all of the samples that tested positive that week – 99 per cent of 786 samples – were infected with influenza A, a common flu virus that causes symptoms such as fever, aches, headaches and diarrhoea.

Health authorities attributed the rise in influenza A cases to factors including low immunity and more movement of people after Covid-19 restrictions were scrapped in December.

In the east, Zhejiang authorities said influenza A had not been prevalent during the coronavirus pandemic.

“The [flu] vaccination rate has been low in the past three years and the population is generally susceptible,” the Zhejiang Provincial Centre for Disease Control and Prevention said in a statement on Tuesday.

“With the adjustment of Covid-19 control measures, crowd mobility and gatherings increased and it is easier for the virus to spread.”

It noted that winter and spring were usually the influenza seasons.