The gunman, who has not yet been identified, shot 10 people before fleeing the station in Brooklyn's Sunset Park neighborhood, law enforcement officials said Tuesday. At least six others were injured in the attack.
The attack took place during Tuesday morning's commute on a subway train in Sunset Park, a southwestern Brooklyn neighborhood that is about a 15-minute train ride to Manhattan.
As a Manhattan-bound N train waited to enter the 36th Street station during rush hour before 8:30 a.m. Tuesday, a man put on a gas mask, took a cannister out of his bag and opened it on the train, filling the train car with smoke, said New York City Police Commissioner Keechant L. Sewell.
The man then opened fire, striking multiple people on the subway and on the platform.
Videos from the scene shared on social media show the smoke-filled train car as passengers flee, some limping off the train. Other videos show bloodied passengers lying on the train platform.
There were currently no known explosive devices on subway trains, Sewell said.
Police were searching for the gunman, described as a Black man with a "heavy build" and who was wearing a green "construction-type vest" and gray hooded sweatshirt, Sewell said Tuesday.
New York Gov. Kathy Hochul urged residents to stay vigilant at Tuesday's news conference and called the incident an "active shooter situation."
"This individual is still on the loose," she said. "This person is dangerous."
In an interview with NY1, Adams said the gunman "appeared to have a planned approach to terrorize our system."
"Getting into the source of why he did what he did, that is something that's going to come out after this investigation is completed," Adams said. "We're taking nothing off the table. We need to apprehend the person, dig into their background and get the details to give the proper classification."
There were 16 people injured in the attack, including 10 people who were shot, said Laura Kavanagh, first deputy commissioner of New York City Fire Department, at a Tuesday news conference. Other injuries resulted from smoke inhalation, shrapnel and "panic," Kavanagh said.
Five of the victims were in critical but stable condition. There were no life-threatening injuries, Sewell said.
No Metropolitan Transportation Authority workers were injured, the New York's Public Transit Union said in a statement.
Sewell said the attack is not currently being investigated as an act of terrorism but did not elaborate.
"We do not know the motive at this time, but we're not ruling anything out," she said.
William Bratton, a former New York Police Department commissioner, said evidence that the attacker may have been motivated by an ideological or political motive may surface later in the investigation, adding that the attack took place in a predominantly Asian community amid a recent rise in violence against Asian American communities.