Cases of respiratory illnesses have been surging in northern China, particularly among children, sparking speculation online of a new pandemic threat four years after COVID-19 first emerged in the country.

However, Chinese health authorities have said the rising infections are a mix of already known viruses and are linked to the country's first full cold season after strict COVID-19 restrictions were lifted last December.

And while emphasizing that the full situation remains unclear, experts say there is little to suggest the cases were caused by a new virus.