Officials said the gunfire wounded at least 10 people, and at least 16 in all were injured in some way in the attack that began on a subway train that pulled into the 36th Street station in the borough's Sunset Park neighborhood.
Five people were in critical condition, New York Fire Department Acting Commissioner Laura Kavanagh said, but Police Commissioner Keechant Sewell said there were no life-threatening injuries.
Sewell added that the attack was not being investigated as terrorism, but that she was ``not ruling out anything.'' The shooter has not been identified.
A train rider's video shows smoke and people pouring out of a subway car. Wails erupt as passengers run for an exit as a few others limp off the train.
One falls to the platform, and a person hollers, ``Someone call 911!'' In other video and photos from the scene, people tend to bloodied passengers lying on the platform, some amid what appear to be small puddles of blood, and another person is on the floor of a subway car.
``My subway door opened into calamity. It was smoke and blood and people screaming,'' eyewitness Sam Carcamo told radio station 1010 WINS, saying he saw a gigantic billow of smoke pouring out of the N train once the door opened.
According to multiple law enforcement sources briefed on the investigation, preliminary information indicated that the gunman who fled was wearing a construction vest and a gas mask.
Investigators believe the gunman deployed a smoke device before opening fire, one of the law enforcement officials said. Investigators are examining whether he may have used that device in an effort to distract people before shooting, the official said.
Fire and police officials were investigating reports that there had been an explosion, but Sewell said at a press conference just after noon that there were no known explosive devices.
Multiple smoke devices were found on the scene, said mayoral spokesperson Fabien Levy.
No MTA workers were physically hurt, according to a statement from the Transport Workers Union Local 100. Besides gunshot wounds, the injured were treated for smoke inhalation, shrapnel and panic.
Juliana Fonda, a broadcast engineer at WNYC-FM, told its news site Gothamist she was riding the train when passengers from the car behind hers started banging on the door between them.
``There was a lot of loud pops, and there was smoke in the other car,`` she said. ``And people were trying to get in and they couldn't, they were pounding on the door to get into our car.''
President Joe Biden and Attorney General Merrick Garland were briefed on the incident, as was Gov. Kathy Hochul. New York City Mayor Eric Adams, who is isolating following a positive COVID-19 test on Sunday, was briefed at the mayor's residence.
The incident happened on a subway line that runs through south Brooklyn in a neighborhood _ predominantly home to Hispanic and Asian communities, about a 15-minute train ride to Manhattan.
Local schools, including Sunset Park High School across the street, were locked down.
Danny Mastrogiorgio of Brooklyn had just dropped his son off at school when he saw a crush of passengers, some of them wounded, running up the subway stairway at the nearby 25th Street station in panic. At least two had visible leg injuries, he said.
``It was insane,'' he told The Associated Press. ``No one knew exactly what was going on.''
Allan Lee was running his business, Cafe Nube, when a half-dozen police cars and fire vehicles suddenly converged on the block that contains the 36th Street station.
``Then they started ushering people that were on the block to the adjacent block and then closed off the subway entrance'' near the cafe's door, he told the AP. When he noticed bomb squad officers and dogs, he was certain it was no everyday subway problem.
A sea of emergency lights was visible from at least a dozen blocks away, where a police cordon was set up.
New York City has faced a spate a shootings and high-profile incidents in recent months, including on the city's subways. One of the most shocking was in January when a woman was pushed to her death in front of a train by a stranger.
Adams, a Democrat a little over 100 days into his term, has made cracking down on crime, especially on the subways, a focus of his early administration, pledging to send more police officers into stations and platforms for regular patrols.
It wasn't immediately clear whether officers had already been inside the station when the shootings occurred.
``We will not allow New Yorkers to be terrorized, even by a single individual,`` Adams said in a taped video message from the mayor's residence, where he was isolating. He did not offer any additional details.