Five people were in a critical but expected to survive. 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.
Police Commissioner Keechant Sewell said the attack was not being investigated as terrorism, but that she was “not ruling out anything.”
The shooter has not been identified and the motive remains unknown.
“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.
The attack unnerved a city on guard about a rise in gun violence and the ever-present threat of terrorism.
It left some New Yorkers jittery about riding the nation’s busiest subway system and prompted officials to increase policing at transportation hubs from Philadelphia to Connecticut.
One rider’s video, shot through a closed door between subway cars, shows a person in a hooded sweatshirt raising an arm and pointing at something – possibly the door to a conductor’s booth – as five bangs sound.
In another video, smoke and people pour out of a subway car and wails erupt as passengers run for an exit while a few others limp off the train.
One falls to the platform, and a person hollers “someone call 911”.
Other videos and photos from the scene show people tending to bloodied passengers lying on the platform, some amid what appear to be small puddles of blood, and another person on the floor of a subway car.
Juliana Fonda, a broadcast engineer at WNYC-FM, told her 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.”
As police searched for the shooter, Governor Kathy Hochul warned New Yorkers to be vigilant.
“This individual is still on the loose. This person is dangerous,” the Democrat said at a news conference.
“This is an active shooter situation right now in the city of New York.”
Fire and police officials were investigating reports there had been an explosion, but Ms 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.
After people streamed out of the train, quick-thinking transit workers ushered passengers to another train across the safety platform, system chief Janno Lieber noted.
High school student John Butsikaris was riding the other train when he saw a conductor urging everyone to get in.
He thought there might just have been a mundane problem until the next stop, when he heard screams for medical attention and his train was evacuated.
“I’m definitely shook,” the 15-year-old told The Associated Press.
“Even though I didn’t see what happened, I’m still scared, because it was like a few feet away from me, what happened.”
No transit workers were physically injured, according to their union. Besides gunshot wounds, the injured riders were treated for smoke inhalation, shrapnel and panic.
President Joe Biden, Vice President Kamala Harris and US Attorney General Merrick Garland were briefed on the incident.
New York Mayor Eric Adams, who is isolating following a positive COVID-19 test on Sunday, said in a video statement that the city “will not allow New Yorkers to be terrorized, even by a single individual.”
The incident happened on a subway line that runs through south Brooklyn in a neighborhood predominantly home to Hispanic and Asian communities and about a 15-minute train ride to Manhattan.
Local schools, including Sunset Park High School across the street from the station, 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 AP.
“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 of 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.
Cr 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 say: No more. No more mass shootings. No more disrupting lives. No more creating a heartbreak for people just trying to live their lives as normal New Yorkers,” Ms Hochul said.