A 19-year-old man was killed on Thursday when a remote-controlled model helicopter that he was piloting in a Brooklyn park struck him in the head, the authorities said.

The man, Roman Pirozek Jr. of Woodhaven, Queens, had been operating the large model — measuring several feet end to end — when it hit him and the top of his head was sliced off, the police said.

The accident occurred around 3:30 p.m. in a grassy area of Calvert Vaux Park that is popular with remote-control helicopter enthusiasts. The cause was not immediately known.

The police were interviewing witnesses in the park, which sits along the Belt Parkway and juts out into Gravesend Bay. The area attracts experienced model helicopter pilots eager to try out new moves with powerful model helicopters that they have often either built themselves or adapted.