Police are searching for a gunman who opened fire inside a Brooklyn subway car on Tuesday morning, injuring more than a dozen people and exacerbating fears in a city already grappling with a surge in crime.

The suspect, wearing a gas mask and green construction vest, first detonated a smoke device aboard a rush hour N train as it pulled into the 36th Street station in Sunset Park headed toward Manhattan, witnesses told police.

As the Manhattan-bound train filled up with smoke, the man began shooting, striking at least 10 people, officials said. Five of the victims suffered critical injuries, though all were expected to survive.

NYU Langone Hospital—Brooklyn reported 21 people were treated at the facility Tuesday for a variety of injuries including gunshot wounds and smoke inhalation. Of those, 16 were discharged and five patients remained in stable condition as of 5 p.m.

Despite initial reports that the suspect had left detonation devices behind, police officials said there was no risk of active explosives within the transit system. Speaking at a press conference on Tuesday afternoon, Gov. Kathy Hochul said New Yorkers should continue to exercise caution.

Police recovered a semiautomatic Glock handgun at the scene which appeared to have been jammed, sources told Gothamist. An alert shared with NYPD officers on Tuesday afternoon asked cops to look out for a U-Haul van with an Arizona license plate and the number AL31408.

"This person is dangerous. We’re asking individuals to be very vigilant and alert,” Hochul said. “This is an active shooter situation right now in the city of New York."

The rush hour mass shooting comes as Mayor Eric Adams has pledged to stem the ongoing rise in gun violence, while at the same time urging New Yorkers to return to in-person work and back onto city subways.

Appearing on CNN Tuesday, Adams said residents should continue to feel safe on their subways. "We can not allow terror to terrorize us so we don't continue to function as a city," said Adams, who is quarantining after testing positive for COVID-19.

Police and emergency responders rushed to the site of a shooting inside of the 36 St subway station

Read more: Stuck in quarantine, Adams weighs in on subway shooting

Witnesses described a chaotic scene as smoke filled the 36th Street subway station and wounded riders stumbled onto the platform.

Juliana Fonda, a broadcast engineer at WNYC, said she was on the N train when she heard gunshots ring out from the neighboring subway car.

“People were pounding and looking behind them, running, trying to get on to the train,” Fonda said. “The door locked between cars and the people behind us — there were a lot of loud pops and there was smoke in the other car.”

As the train pulled into the 36th Street station, transit riders attempted to flee the train onto an opposite R train, according to Joanna, a Bay Ridge resident. She shared photos of wounded riders lying on the floor of the subway car, as the 36th Street station filled up with smoke.

"Two doctors came running from other cars to help two people bleeding out in my car,” Joanna, who declined to give her last name, told Gothamist. ”Nobody saw who did it, everyone thought it was a bomb.”

“It was mayhem and chaos,” she added.

The MTA warned of delays on the B, D, F, N, Q, and R lines as a result of a “major disruption to service.” Authorities have urged residents to avoid the area of 36th Street and 4th Avenue.

A shelter-in-place order for schools in District 15 was lifted for many schools shortly after noon on Tuesday.

White House spokesperson Jen Psaki said President Biden had been briefed on the attack.

"White House senior staff are in touch with Mayor Adams and Police Commissioner Sewell to offer any assistance as needed," she said.

This is a breaking story and will be updated as more information becomes available.

Correction: A previous version of this story misstated the day of the incident.