The child's name, hometown and other details will not be released to protect the privacy of the child and the family, NJ Health Commissioner Judy Persichilli said.
The child had an underlying medical condition, Gov. Phil Murphy added.
"It's the only fatality we've had under the age of 18," he said. "We're going to leave it at that."
The news comes days after 15 New York City children were reported to have contracted Kawasaki disease, an inflammatory illness possibly associated to COVID-19. State health officials said Thursday that at least 12 New Jersey hospitals have treated children with the rare disease.
It is unknown whether the child announced Friday had the disease.
“I think we’ve said all we’re gonna say about the blessed 4-year-old we’ve lost,” Murphy said.
Children contracting coronavirus is rare. The federal Centers for Disease Control and Prevention (CDC) data suggested last month that children represent only 2 percent of all U.S. cases and their COVID-19 symptoms tend to be milder than those found in adults.
New Jersey has 1,985 new positive cases as of Friday, meaning the state has had a total of 135,454 residents with coronavirus.
There were 4,606 coronavirus patients in hospitals, Persichilli said, including 1,439 in critical care and 1,089 on ventilators as of Friday.
A total of 514 long-term care (LTC) facilities now have reported positive COVID-19 cases -- for a total of 25,254 nursing home patients testing positive and 4,691 deaths.
Statewide, a total of 8,952 NJ residents have died of coronavirus, Murphy said, including 162 deaths confirmed since Thursday.
A 12th state psychiatric hospital patient also has died of coronavirus, Persichilli said. A total of 177 of the state's 1,250 psychiatric patients have tested positive for COVID-19, she said.
A total of 362 of the 673 residents of state veterans' homes have tested positive for COVD-19 including 127 deaths, she said.
"They are the faces of those we have seen everyday and they should remain in our thoughts,'' Murphy said. "In all of World War II, we lost 12,600" military personnel from New Jersey.
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