He said in his Facebook posting today that the condition causes inflammation in the blood vessels and symptoms like fever and rashes.
Meanwhile, WHO director-general Dr Tedros Adhanom Ghebreyesus said reports from Europe and North America have described a small number of children being admitted to intensive care units with a multisystem inflammatory condition with some features similar to those of Kawasaki disease and toxic shock syndrome.
“It is urgent to carefully characterise this clinical syndrome and its risk factors, to understand causality and to describe treatment interventions.
"I have called on clinicians worldwide to work with their national authorities and WHO to be on the alert and better understand this syndrome in children,” he said in a WHO short video clip which was also shared by Dr Noor Hisham.
In the same video clip, COVID-19 technical lead for WHO's Health Emergencies Programme, Dr Maria Van Kerkhove noted it is a very rare condition and WHO has been getting a description of the symptoms that were not always the same in children tested positive for COVID-19.
According to the official WHO website, case reports and small series have described a presentation of acute illness accompanied by a hyperinflammatory syndrome, leading to multiorgan failure and shock.
It is not yet clear the full spectrum of disease, and whether the geographical distribution in Europe and North America reflects a true pattern, or if the condition has simply not been recognised elsewhere.