New York, New York - Four people including a police officer were killed Monday after a gunman walked into a skyscraper in Midtown Manhattan and opened fire in broad daylight.

A fifth victim was also in critical condition after being shot, while the suspect apparently took his own life, Mayor Eric Adams told a late-night briefing at a hospital near the scene of the shooting.

The gunman was caught on camera exiting a black BMW carrying an M-4 rifle, then entering the building, immediately opening fire on a police officer before "spraying the lobby" with bullets, police commissioner Jessica Tisch told the press conference.

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

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The office tower block at 345 Park Avenue is also home to hedge fund giant Blackstone, auditor KPMG, and the NFL.

Tisch told the briefing that the suspect was believed to have acted alone but inquiries were ongoing, with the FBI assisting in the investigation.

She identified the shooter as Shane Tamura of Las Vegas and said a revolver, ammunition and magazines were found in his vehicle along with medication bearing his name.

The man had a history of mental health issues according to Las Vegas law enforcement, but did appear to possess a valid firearms permit for Nevada, Tisch said.

He drove cross-country from the southwestern state in recent days and arrived in New York on Monday.

The incident began around 6:00 PM 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, while another described a gunman going floor to floor as staff prepared to leave for the day.

Adams said the fallen police officer, an immigrant from Bangladesh who was 36 years old, was among the dead.

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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.

"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."

There have been 254 mass shootings in the United States this year, according to the Gun Violence Archive, which defines a mass shooting as four or more people shot.

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

The frontrunner in the race for mayor Zohran Mamdani wrote on X that he was "heartbroken to learn of the horrific shooting in midtown" and was "holding the victims, their families, and the NYPD officer... in (his) thoughts."