LONDON (REUTERS) - Doctors in France and northern Italy, one of the areas hardest hit by the new coronavirus, have reported spikes in cases of a rare inflammatory syndrome in young children that appears similar to one reported in the United States, Britain and Spain, according to a report in The Lancet.

The condition, "Pediatric Multi-System Inflammatory Syndrome Potentially Associated with Covid-19," shares symptoms with toxic shock and Kawasaki disease including fever, rashes, swollen glands and, in severe cases, heart inflammation.

Reports of cases have raised concerns that Covid-19, the disease caused by the novel coronavirus, could pose a greater risk to children than had been understood.

Covid-19 so far has taken its greatest toll on the elderly and those with chronic health conditions.

New York on Sunday said it was investigating up to 85 cases of children with the syndrome. So far three of those children, who also tested positive for Covid-19, have died, and two more deaths are under review, Governor Andrew Cuomo said.

In Bergamo, Italy, between Feb 18 and April 20, the Hospital Papa Giovanni XXIII admitted 10 children with the syndrome, including eight who tested positive for coronavirus antibodies.

Over the last five years, doctors there had seen a total of only 19 children with Kawasaki disease, according to the report published by The Lancet late on Wednesday (May 13).

Compared to children with Kawasaki disease in the past, those they saw during the pandemic were older and more severely ill, the report said, with 60 per cent suffering heart complications and half having signs of toxic shock syndrome.

French researchers on Thursday reported Kawasaki disease-like symptoms in 17 children admitted to a Paris hospital between April 27 and May 7, while in an average two-week period they would have expected to see only one such case.

The report, by Dr Martin Chalumeau of Necker Hospital for Sick Children, has not been peer reviewed. It was posted on the medRxiv website, which has been a major source of research on Covid-19 before official publication.

Scientists are still trying to determine whether the syndrome is linked with the new coronavirus because not all children with it have tested positive for the virus.

Some researchers have suggested the coronavirus family might trigger Kawasaki disease.

"The symptoms in children are different from adults with Covid-19 in whom the illness is more of a respiratory condition," said Dr George Ofori-Amanfo, division chief of Paediatric Critical Care at Mount Sinai Kravis Children's Hospital, New York.

Children with the rare inflammatory syndrome often have severe abdominal pain and vomiting that progresses to shock, Ofori-Amanfo told Reuters.

He said none of the children he has seen recently with this syndrome had any underlying disease, but they all had antibodies for the coronavirus.