Beijing, China - The World Health Organization has asked China for more data on a respiratory illness spreading in the north of the country, urging people to take steps to reduce the risk of infection.

Northern China has reported an increase in "influenza-like illness" since mid-October when compared to the same period in the previous three years, the WHO said.

"WHO has made an official request to China for detailed information on an increase in respiratory illnesses and reported clusters of pneumonia in children," the UN health body said in a statement on Wednesday.

China's National Health Commission told reporters last week that the respiratory illness spike was due to the lifting of Covid-19 restrictions and the circulation of known pathogens, like influenza and common bacterial infections that affect children, including mycoplasma pneumonia.

Beijing is currently experiencing a cold snap, with temperatures expected to plummet to well below zero by Friday, state media said.

The city has "entered a high incidence season of respiratory infectious diseases", Wang Quanyi, deputy director and chief epidemiological expert at the Beijing Center for Disease Control and Prevention, told state media on Wednesday.

Beijing "is currently showing a trend of multiple pathogens coexisting," he added.

At Beijing's Capital Institute of Pediatrics' Children's Hospital on Thursday, AFP journalists saw crowds of parents and children dressed in winter clothes.

A parent named Zhang accompanied her coughing nine-year-old son and said he had fallen ill with pneumonia.

"There are really a lot of children who have caught it recently," she said.

Li Meiling (42) had brought her eight-year-old daughter, who was suffering from mycoplasma pneumonia – a pathogen that can cause sore throats, fatigue, and fever.

"It's true that a lot of children her age are ill with this at the moment," she told AFP.

But she said she was "not particularly worried" about the WHO announcement.

"It's winter, so it's normal that there are more cases of respiratory illnesses. It's due to the season."

On November 21, media and public disease surveillance system ProMED reported clusters of undiagnosed pneumonia in children in northern China.

The WHO said it was unclear if ProMED's report was related to the authorities' press conference and that it was seeking clarification.

The agency "has also requested additional information on recent trends in the circulation of known pathogens, including influenza, SARS-CoV-2 (the virus that gives rise to Covid-19), RSV affecting infants and Mycoplasma pneumoniae, as well as on the degree of overcrowding in the health system," the statement added.

In the meantime, it urged people to take preventative measures, including getting vaccinated, keeping distance from sick people and wearing masks.

Over the course of the Covid-19 pandemic, the WHO repeatedly criticized Chinese authorities for their lack of transparency and cooperation.