Police are searching for the man they say is responsible for stabbing a 44-year-old man in the head aboard a northbound J train, leaving him fighting for his life.

They say the attack happened during a fight on Jan. 24, just before 8 p.m., as the train approached the Broadway/Myrtle Avenue subway station.

The attacker pulled out a sharp object and stabbed the 44-year-old in the head before running from the scene.

EMS took the 44-year-old to NYC Health and Hospitals/Brookdale in critical condition, according to authorities.

The man was last seen wearing black clothing, white and black sneakers, a maroon baseball hat, and carrying a black bookbag.

Anyone with information is urged to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477).