The NYPD identified a person of interest in today's Brooklyn subway shooting as a man named Frank James. Investigators stressed, however, that they do not know if James has any connection to the shooting. 

Earlier in the day, a gunman in a gas mask and construction vest set off a smoke grenade and fired a barrage of at least 33 bullets in a rush-hour subway train, shooting at least 10 people Tuesday, authorities said. Police were scouring the city for the shooter and trying to track down the renter of a van possibly connected to the violence.

A scene of horror unfolded as frightened commuters ran from the train as others limped out of it. At least one rider collapsed on the platform.

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, according to hospitals.

The gunfire erupted on a train that pulled into a station in the 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’s motive was unknown.

Authorities found a 9 mm semi-automatic handgun at the scene, along with extended magazines, a hatchet, both detonated and undetonated smoke grenades, a black garbage can, a rolling cart, gasoline and key to a U-Haul van, Chief of Detectives James Essig said.

He said the key led investigators to the van renter, who they identified as James and said has addresses in Philadelphia and Wisconsin. Authorities were looking for him, but Essig stressed that it wasn’t yet clear whether the man was linked to the shooting.

Investigators believe the weapon jammed, preventing the suspect from continuing to fire, the officials said. The federal Bureau of Alcohol, Tobacco, Firearms and Explosives has completed an urgent trace to identify the gun’s manufacturer, seller and initial owner.

The officials said authorities zeroed in on a person of interest after the credit card used to rent the van was found at the shooting scene.

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.

The Metropolitan Transportation Authority announced last fall that it had put security cameras in all 472 subway stations citywide, saying they would put criminals on an “express track to justice.” But at the station where the train arrived, the cameras apparently weren’t working.

MTA system chief Janno Lieber told TV interviewers he didn’t know why the cameras malfunctioned. But he said police had “a lot of different options” from cameras elsewhere on the subway line to get a glimpse of the shooter.

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 as five bangs sound. In another video, smoke and people pour out of a subway car, some limping.

“Someone call 911!” a person shouts.

Other video 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.

Rider Juliana Fonda, a broadcast engineer at WNYC-FM, told its news site Gothamist that passengers from the car behind hers started banging on the connecting door.

“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, Gov. 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 just after noon. “This is an active shooter situation right now in the city of New York.”

Fire and police officials had responded to reports of an explosion, but Sewell said at the press conference that there were no known explosive devices. Multiple smoke devices were found on the scene, mayoral spokesperson Fabien Levy said.

After people streamed out of the train, quick-thinking transit workers ushered passengers to another train across the platform for safety, Lieber, the MTA chairman, noted.

High school student John Butsikaris was riding the other train when he saw a conductor urging everyone to get in. He thought it might be 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 hurt, according to their union.

In Menlo, Iowa, President Joe Biden praised “the first responders who jumped in action, including civilians, civilians, who didn’t hesitate to help their fellow passengers and tried to shield them.”

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.”

New York City has faced a spate of shootings and high-profile bloodshed 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 were already inside the station when the shootings occurred.

Danny Mastrogiorgio of Brooklyn had just dropped his son off at school when he saw a crush of panicked passengers, some wounded, running up the stairway at the 25th Street station. At least two had visible leg injuries, he said.

“It was insane,” he told the AP. “No one knew exactly what was going on.”