Firefighters called to extinguish a boat fire in Brooklyn were shocked to find a dead man onboard, officials said.

The episode unfolded at 6:15 a.m. Saturday when cops and firefighters responded to a 911 call regarding a boat blaze at Pier 5 Marina in Brooklyn Bridge park, the NYPD said.

Upon arrival, firefighters doused the flames on the 52-foot Jefferson Recreational boat, but upon closer look an 86-year-old man was found “unconscious and not responsive” in the hull, police said.

The man was pronounced dead at Kings County Hospital.

The investigation is ongoing, and the city medical examiner will determine the cause of death, said police, who withheld the man’s identity pending family notification.

Anyone with information is asked to call the NYPD’s Crime Stoppers Hotline at 1-800-577-TIPS (8477) or for Spanish, 1-888-57-PISTA (74782).