Three Children have Died of a mysterious Syndrome Linked to the Coronavirus.

Three young children have died in New York of a mysterious, toxic-shock inflammation syndrome with links to the coronavirus, Gov. Andrew M. Cuomo said on Saturday.

“The illness has taken the lives of three young New Yorkers,” Mr. Cuomo said during his daily briefing in Manhattan. “This is new. This is developing.”

As of Saturday, more than 73 children in New York have been sickened by the rare illness, which has some similarities to Kawasaki disease and was publicly identified for the first time earlier this week.

Governor Cuomo said many of these children, some as young as toddlers, did not show respiratory symptoms commonly associated with the coronavirus when they were brought to area hospitals, but all of them tested positive either for Covid-19, the disease caused by the coronavirus, or for its antibodies.

“So it is still very much a situation that is developing, but it is a serious situation,” he added.

The state will be working with the New York Genome Center and Rockefeller University to determine what is causing the illness, which Governor Cuomo described on Saturday as “truly disturbing.”

When the coronavirus pandemic began ravaging the New York area two months ago, the state found solace in the initial evidence that children would be largely unaffected. That sense of relief was shattered this week when a 5-year-old died in New York City of the newly discovered disease, which doctors described as a “pediatric multisystem inflammatory syndrome.” The inflammation of the blood vessels, Mr. Cuomo said, causes “problems with their heart.”

Mr. Cuomo did not elaborate on the deaths of the two additional children.

“We were laboring under the impression that young people were not affected by Covid-19, and that was actually good news,” Mr. Cuomo said. “We still have a lot to learn about this virus.”

Mr. Cuomo has asked parents to be vigilant in looking for symptoms such as prolonged fever, severe abdominal pain, change in skin color, racing heart and chest pain.

Before the announcement of the deaths attributed to the new illness, fewer than four children under age 10 had died of the virus in New York, according to the most recent breakdown from the state. Mr. Cuomo said the state was working with the Centers for Disease Control to determine if the confounding illness had been affecting children infected with the virus before this week.

“It is very possible that this has been going on for several weeks and it hasn’t been diagnosed as related to Covid,” he said.

Mr. Cuomo also announced 226 more deaths due to the coronavirus, 10 more than the number reported a day earlier.

“That number has been infuriatingly constant,” he said. “We would like to see that number dropping at a faster rate that it is currently dropping.”

Despite the setbacks, New York continued to make inroads in its fight against the coronavirus, Mr. Cuomo said.