An investigation is underway after a 4-year-old never woke up from a nap at a New Jersey preschool.

Staff at the Cordero School in Jersey City found the boy unresponsive after he took an afternoon nap Thursday.

The boy was rushed to a hospital, where he was pronounced dead.

Principal Derek Stanton said in letter to parents that they will have grief counselors at the school Friday.

The boy's name has not been released.

There is no indication of foul play.