New York, Apr 13 (IANS): The New York City Police Department (NYPD) said that they were seeking Frank James, a "person of interest", in connection to a subway shooting in New York City's Brooklyn that left more than 20 people injured.

"Mr. James is just a person of interest we know right now who rented that U-Haul van in Philadelphia," NYPD's Chief of Detectives James Essig said at a press conference on Tuesday night.

The police said a key to the van was found in a collection of belongings on the train that they believe belonged to the gunman, Xinhua news agency reported.

"We are endeavouring to locate him to determine his connection to the subway shooting, if any," Essig said.

The authorities are offering a $50,000 reward for any information leading to the arrest of the suspect involved in the shooting.

During the rush hour on Tuesday morning, a man opened fire and threw a smoke canister aboard the moving train, according to the police.

The Fire Department said that five victims were in critical condition, but none were believed to have suffered life-threatening injuries.

The attack triggered a massive law enforcement response to Brooklyn's Sunset Park neighbourhood and a manhunt for the suspect.

The gunman, who police said was wearing a construction vest and gray hooded sweatshirt, was using a handgun, and fled the scene. Any possible motive was still unknown.

Tuesday's attack came as the city is struggling to cope with a rise in shootings. Citywide shooting incidents increased by 16.2 per cent in March from a year ago, showed NYPD data.