Authorities are searching for a man who they say stabbed two children — one of them fatally — inside an elevator at an apartment building in Brooklyn.

Officers arriving at the housing development in the East New York neighborhood just before 6 p.m. Sunday found a 6-year-old boy — identified as Prince Joshua Avitto — in the elevator and the other victim, a 7-year-old girl, just outside the building, police said.

Both children were taken to Brookdale Hospital, where the boy was pronounced dead. The girl was moved to New York-Presbyterian Hospital/Weill Cornell Medical Center, where she was listed in critical condition, police said. The children were not related.

Police did not say what may have led to the violence. A knife was recovered at the scene.

"He took my pride and joy away," the boy's father, Nicholas Avitto, told the Daily News. "I'm devastated. I'm beyond comprehension. I'm trying to understand how God works. My son is gone. That was the light of my life."

A resident, Kevin Velez, 41, told the New York Post "it was just a normal day with kids running around. And then it became chaos."

Velez said he witnessed the boy being taken out of the building.

"He was lifeless, just lifeless," he said.

Police said it did not appear that a fatal stabbing of an 18-year-old woman on Friday a few blocks away was related to Sunday's violence.