New York's Mayor Bill de Blasio has voiced "tremendous concern" over an uptick in cases of a paediatric syndrome that scientists suspect could be linked to Covid-19.
The mayor said there have been 38 cases of paediatric multi-system inflammatory syndrome detected in New York City, with an additional nine suspected cases awaiting confirmation.
There have been three deaths statewide linked to the syndrome, Governor Andrew Cuomo had said over the weekend, with one in the city.
Symptoms of the syndrome include persistent fever, rash, abdominal pain and vomiting.
"What it does is, basically, in a child's body triggers an intensive, almost overwhelming immune system response. And that actually causes harm to the body," Mr de Blasio said.
The mayor said all children with associated symptoms would now be tested for Covid-19 as well as antibodies.
So far, of the confirmed cases, 47% had tested positive for coronavirus and 81% had antibodies, indicating exposure to the fast-spreading virus at some point.
Mr de Blasio urged all parents whose children exhibited the symptoms to seek immediate medical attention.
On Friday, Mr Cuomo had reported at least 73 children throughout New York state had developed the rare illness, which has some similarities to Kawasaki disease.
Kawasaki disease is a mysterious illness that primarily affects children up to the age of five and causes the walls of arteries to become inflamed, resulting in fever, skin peeling and joint pain.
Britain's National Health Service first sounded the alarm last month, warning about a small rise in children infected with the coronavirus that have "overlapping features of toxic shock syndrome and atypical Kawasaki disease."
France has also reported several cases.
Though frightening, most recover without serious issues.