The World Health Organization has asked China for more data on respiratory illnesses spreading in the north of the country, but Beijing offered no public comment on Thursday.
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 U.N. health body said in a statement on Wednesday.