A gunman with mental health issues opened fire in a central Manhattan skyscraper on Monday, killing four people including a policeman before apparently taking his own life, officials said.

A fifth victim was in critical condition after being shot, Mayor Eric Adams told a late-night press briefing at a nearby hospital.

The gunman was caught on surveillance footage leaving a black BMW and carrying an M-4 rifle, police commissioner Jessica Tisch told the news conference.

On entering the building, he immediately opened fire on a police officer before "spraying the lobby" with bullets, she said.

The gunman then took an elevator to the 33rd floor of Rudin Management, which owns the building, and continued his spree before apparently shooting himself. He was later discovered by officers next to his weapon.

The office tower block at 345 Park Avenue -- home to the National Football League, hedge fund giant Blackstone, and auditor KPMG -- was apparently targeted by the gunman, who is believed to have acted alone, Tisch said.

The police commissioner gave the shooter's name as Shane Tamura from Las Vegas and said a revolver, ammunition and magazines were found in his vehicle. 

Tamura had a history of mental health issues, she said.

The incident began around 6:00 pm (2200 GMT) when reports of gunfire prompted hundreds of police to swarm a busy office district on the storied Park Avenue, an area popular with tourists and visiting businesspeople.

A worker from a nearby office building wept as she left the area after a local lockdown was lifted.

'Senseless'

Another described the gunman going floor to floor as staff prepared to leave for the day.

"We lost four souls to another act of senseless violence," the city's mayor said, excluding the shooter who also died, apparently by a self-inflicted gunshot.

Adams said the fallen police officer was a 36-year-old immigrant from Bangladesh.

Two other males and a female died and another man remained in a critical condition, officials said without giving any preliminary motive for the shootings.

Office worker Shad Sakib told AFP that he was packing his things to leave work when a public address announcement warned him and his colleagues to shelter in place.

"Everyone was confused with like, 'wait, what's going on?' And then someone finally realized that it's online, that someone walked in with a machine gun," the witness said.

'Floor by floor'

"He walked right into a building right next door. We saw the photo of him walking through the same area that I walked through to get lunch here.

"You would think it won't happen to you, and then it does."

Another witness, a woman who declined to give her name as she left the vicinity of the shooting, told AFP: "I was in the building. He went floor by floor." 

A second woman wept as she left the scene. 

There have been 254 mass shootings in the United States this year including Monday's incident in New York, according to the Gun Violence Archive -- which defines a mass shooting as four or more people shot.

Police deployed a drone near Park Avenue at the height of the evening rush hour as dozens of officers swarmed the area, some carrying long guns and others wearing ballistic vests.

Police repeatedly pushed back journalists and members of the public who gathered to see what was happening in the normally calm but busy area of Midtown Manhattan.

The area is home to several five-star business hotels, as well as a number of corporate headquarters and financial and law firms. The United Nations headquarters is nearby.

New York Governor Kathy Hochul said she has been briefed on the shooting.

Zohran Mamdani, the frontrunner in the forthcoming New York mayoral race, wrote on social media that he was "heartbroken to learn of the horrific shooting in midtown and I am holding the victims, their families, and the NYPD officer... in my thoughts."