Officials have said at least 16 people were injured during the attack at the 36th Street station in Brooklyn's Sunset Park area.

Five people are in a critical but stable condition, according to the New York Fire Department commissioner.

New York Police Commissioner Keechant Sewell confirmed ten people were shot but did not saying how the other six people sustained their injuries.

Ms Sewell also said the attack is not being investigated as terrorism and confirmed there were no life-threatening injuries.

The suspect was reported as being a Black male with a heavy build, wearing a green construction-type vest and a hooded sweatshirt, Ms Sewell added.

"This morning, as a Manhattan-bound N train waited to enter the 36th station, an individual on that train donned what appeared to be a gas mask, he then took a canister out of his bag and opened it," the police commissioner told a press conference.

"The train at that time began to fill with smoke. He then opened fire, striking multiple people on the subway and in the
platform," Ms Sewell added.

Video has shown smoke billowing out of the train carriage as it pulled into the station and opened its doors, with passengers pouring out and some collapsing to the ground.

Photos shared on social media show people tending to bloodied passengers lying on the floor.

US President Joe Biden has been briefed on the developments and senior staff are in contact with the city's mayor, Eric Adams, White House press secretary, Jen Psaki said.

Eyewitness, Sam Carcamo, told radio station 1010 WIN he saw a gigantic billow of smoke pouring out of the train once the door opened.

"My subway door opened into calamity. It was smoke and blood and people screaming", he said.

A video captured by a bystander shows people lying on the subway platform amid what appeared to be small puddles of blood, as a loudspeaker announcement told everyone on the smoke-hazy platform to get on a train.

Outside the station a police officer yelled: "Let's go! Get out of the way!"

The incident happened on a subway line that runs through south Brooklyn in a neighbourhood about a 15-minute train ride to Manhattan.

Local schools, including Sunset Park High School across the street, were locked down.

Video footage also showed a large law enforcement presence around the subway station, including heavily armed officers and dozens of police cruisers and emergency vehicles.

It was not immediately clear whether officers had already been inside the station when the shootings occurred.

Outside the 36th Street station, in an area known for its thriving Chinatown and views of the Statue of Liberty, authorities shut down a dozen or so blocks and closed off the immediate area with yellow crime scene tape.