Ten people were shot when a gunman filled a rush-hour subway train with smoke and opened fire in Brooklyn, New York.
Photos from the scene showed people tending to bloodied passengers lying on the station floor.
Five people were in critical condition but expected to survive. At least 29 in all were treated at hospitals for gunshot wounds, smoke inhalation and other conditions.
New York Police Commissioner Keechant Sewell said there was no known link to terrorism and there were no known explosive devices at the scene.
Warning: This story contains graphic images
"This morning, as a Manhattan-bound N train waited to enter the 36th [Street] 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," Ms Sewell said at a press conference.
The gunman sought in the attack was "still on the loose" and dangerous, New York Governor Kathy Hochul said.
She added that the suspect was reported to be a black male with a heavy build, wearing a green construction-type vest and a hooded sweatshirt.
Police found an abandoned U-Haul van in Brooklyn matching the description and licence plate number of the vehicle being sought in connection with the shooting, a law enforcement official said.
Police closed off a street about 6 kilometres from the shooting scene and cleared nearby businesses while waiting for the bomb squad and a highly-specialised emergency services unit.
Authorities had a photo of a suspect and were working to confirm his identity, two law enforcement officials said.
The motive remains unknown.
Investigators recovered a handgun at the scene, along with multiple smoke devices and other items they are analysing, the officials said.
Investigators believe the weapon jammed, preventing the suspect from continuing to fire, the officials said.
Security cameras apparently malfunctioned in the station where the train arrived, Mayor Eric Adams told WCBS-AM.
'It was insane', witness says
Witnesses described scenes of panic and chaos on the subway.
Danny Mastrogiorgio had just dropped his son off at school when he saw a crush of passengers, included multiple wounded people, running up the subway stairway at the 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."
Outside the 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.
Students and staff at all schools in the neighbourhood were directed to shelter in place.
John Butsikares, a 15-year-old who passed through the 36th Street station soon after the incident, said the train conductor ordered everyone on the station platform to get on board.
"I didn't know what happened. It was a scary moment. And then at 25th Street [the next station] we were all told to get off. There was people screaming for medical assistance," he said, adding that he had been going to school.
"It was just a scary moment. It was, everyone was packed together, and I didn't know what happened until after."
Allan Lee was running his business, Cafe Nube, when police cars and fire vehicles suddenly converged on the block.
"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.
Trains servicing that station were delayed during the morning commute.
Ms Hochul said she had been briefed on the situation and her office would work with the transit authority and police department as the investigation continued.
"We will not allow New Yorkers to be terrorised, even by a single individual," said New York City Mayor Eric Adams.
Wires/ABC
