A manhunt is underway for a man who is believed to have set a woman sleeping in a subway car on fire, leading to her death.

The woman, who was not identified, was asleep on an idle F train Sunday morning at the Stillwell Avenue station in Brooklyn just before 7:30 a.m., the New York Police Department said. It was there that a man approached her, lit her on fire, and fled the subway, police said.

Police are investigating it as a…