[WATCH] New York police seek 'person of interest' in subway shooting that left more than 20 injured

New York City police have named "a person of interest" in connection with a subway station shooting in Brooklyn on Tuesday that left more than 20 people injured.

Police said they were looking for Frank R James, 62, since he had rented a U-Haul van they believe may be linked to the shooting. The key to the van, rented in Philadelphia, was found at the scene.

James has not been named as a suspect but police believe he may have information about the shooting which happened during morning rush hour.

"We are looking to determine if he has any connection to the train," NYPD Chief of Detectives James Essig said, calling on anyone with information on his whereabouts to call a hotline.

A photo of 'person of interest' Frank R James released by the New York police

More than 20 people were injured, several of them with gunshot wounds, after a smoke grenade was detonated in the subway followed by shots.

The attacker, who wore a green construction vest and grey sweatshirt, fled the scene and remains at large. The attack happened at around 8:30am local time during rush hour when police responded to an emergency call after one of the carriages of a train arriving at Brooklyn station filled with smoke.

During a press conference, police said the incident is not being investigated as an act of terrorism but a motive has not been established.

"Fire personnel responding to reports of smoke at the 36th Street station in the Sunset Park neighbourhood found multiple people shot and undetonated devices," a Fire Department spokesperson said earlier.

Photographs and videos shared on social media from the scene showed people tending to passengers covered in blood lying on the floor of the station.

The New York subway lines were shut and scores of police and medical teams were rushed to the scene. People were warned to stay away from the area near 36th Street station in the Sunset Park neighbourhood.