A man who allegedly threatened to "shoot up" an Upper East Side hospital was fatally shot by New York City police officers Thursday evening.

Police said the suspect, identified as 20-year-old Elijah Brown, had no history of interactions with the NYPD before an encounter at Mount Sinai Medical Center led to a crime scene spanning nearly a dozen city blocks. 

Surveillance video obtained by CBS News New York shows the suspect walking down Madison Avenue with what appears to be a gun in hand.

With their weapons drawn, officers start running after him.

A different angle shows the suspect turning around and appearing to raise his weapon at them. Police said the suspect fired first at the officers, forcing them to shoot back.    

"The situation could have turned out differently," NYPD Chief of Patrol Philip Rivera said. "An individual walked into multiple locations with a gun, menaced multiple people with that gun, and then shot at our officers in the middle of a busy sidewalk with civilians in close proximity."   

"Call 911. I'm going down to the hospital to shoot it up."

Police said the crime spree started at around 7 p.m. inside a residential building on Madison Avenue on East 107th Street.

Police said Brown threatened a man at gunpoint in the elevator of his own apartment building. Brown got off the elevator on the first floor and left the building, police said.

"I never got into nothing with him, but I know something's wrong - the way he moves," a neighbor of Brown's said.

A woman who wanted to remain anonymous said a security guard showed her surveillance video of Brown threatening the man in the elevator.

"The old man put his hand up to the gun, and I guess he was saying, 'Don't shoot me,'" she said.

Brown then went to a deli at Madison Avenue and East 107th Street, where police say he went behind the counter and pointed a gun at a deli worker.

The suspect allegedly told the deli worker, "Call 911. I'm going down to the hospital to shoot it up," according to police.

Brown then stole the deli worker's phone and left the deli, police said.

Deli worker Muhsin Alsadi said a cook and his teenage brother were working at the time.

"Thank God he was safe. All I thought about was that he was safe, and that was all," he said.

Suspect entered Mount Sinai Hospital

Police said around 7:08 p.m., the suspect briefly entered Mount Sinai Medical Center, but then went back outside and placed a firearm on the ground next to a tree.

The suspect then went back inside the hospital, where he encountered an off-duty NYPD officer who was working a security detail, police said.

According to police, the suspect was acting disorderly and said he had a gun.

When the off-duty NYPD officer tried to escort him out, police said a struggle ensued.

"It was said that someone had a gun in the lobby," pediatric emergency nurse Donovan James Carey said. "My first thought was just, I have to protect these kids. So we got everyone inside, and I held the door until we got a message that it was clear."

Brown went back outside, picked the gun up and began walking southbound on Madison Avenue.

"All of a sudden, you just see a gun come out"

Police said the off-duty NYPD officer requested assistance, and responding officers spotted the armed suspect on Madison Avenue between East 96th and 95th streets.

According to police, as soon as the officers exited their vehicles, the suspect opened fire. Police said multiple bystanders who had just gotten off an MTA bus were nearby at the time.

"He was, like, near the bus stop, and then it was like a scuffle with someone else. And then all of a sudden, you just see a gun come out, and then, like, shooting," witness Layla Helou said.

The officers returned fire, striking the suspect, police say. According to police sources, Brown was shot in the hip and chest.

Suspect pronounced dead at hospital

Officers drove the suspect back to the same hospital he just threatened, where he was pronounced dead.

"We're not even a trauma hospital, but every single nurse did everything that they could to save his life, no questions asked. And I think that speaks to the quality of character of the nurses, that we do our best for every single patient that comes through the doors, no matter what the situation is," Carey said. 

"Every day our officers put on their uniforms and they encounter dangerous situations across this city, but it's another kind of danger when someone goes into a deli and a hospital with a gun and opens fire directly at the NYPD," Rivera said. "This is the risk that every member of the NYPD faces every single day to keep this city safe."  

Police said no involved officers were injured, but they were taken to a local hospital for evaluation. No bystanders were hurt either, officials said. 

A loaded gun was recovered at the scene, investigators said.