A construction worker died on the job in Brooklyn Friday when falling debris hit him on the head, sending him plunging down a shaft, cops said.

Alex Santizo, 21, was working inside a private home on 45th Street in Borough Park when the accident happened at about 2:15 p.m.

He fell from the second to the first floor of the building.

He was rushed to Maimonides Medical Center, where he was pronounced dead.

The building has seven open ­violations with the city’s Department of Buildings, including one that is considered “hazardous,” agency ­records indicate.