NYPD and MTA officials said a 36-year-old man was critically injured in a shooting Thursday afternoon at a subway station in Downtown Brooklyn.

NYPD Chief of Transit Michael Kemper said it happened at around 4:45 p.m. on a northbound A train at the Hoyt Schermerhorn station.

Officials said the victim was shot in the head. They said he underwent surgery and was listed in critical condition as of Thursday night.

Police were trying to determine as of Thursday night if the incident was a crime or a case of self-defense.

Kemper said detectives believe a 32-year-old man boarded the train at Nostrand Avenue. He said a 36-year-old man who was already on the train approached the 32-year-old.

Several witnesses described the 36-year-old as aggressive and provocative toward the 32-year-old. Kemper went on to say words were exchanged and the 36-year-old took out a knife or razor blade which was eventually dropped. The two men calmed down but then fought again.

Kemper said the 36-year-old took out a gun, the two got into a physical altercation, the 32-year-old got a hold of the gun and fired multiple shots, striking the 36-year-old.

As this was occurring, Kemper said the train was arriving at the Hoyt Schermerhorn subway station. He reiterated that there were multiple officers already at the station who heard the shots and responded to the scene to provide medical assistance.

He said the officers called for an ambulance and gathered witnesses.

MTA Chair and CEO Janno Lieber called the incident "outrageous." He praised Mayor Eric Adams and Gov. Kathy Hochul for their efforts to curb gun violence.

Lieber added that the subways are "no place for guns."

Police said the 32-year-old man, who they believe pulled the trigger, is in custody. They say he is a person of interest.

Detectives were still investigating and speaking with witnesses as of Thursday night to determine if the person of interest in police custody will face charges or not.