A gunman opened fire Monday outside a midtown Manhattan building that houses the National Football League offices and some of the country’s top financial firms, killing an off-duty New York City police officer working security in the building and four others, sources told The Associated Press.

The suspect was identified as Shane Tamura, of Nevada, two people briefed on the investigation told the AP. Law enforcement officials found identification on Tamura’s body, including a concealed carry permit from Las Vegas, the people said.

Police sources told ABC News they believe the suspect later died from a self-inflicted gunshot wound after fleeing into the 44-story building at 345 Park Avenue. Upon entering the lobby, he fired at the police officer, who was working private security at the time he was shot and killed, before apparently killing himself after being barricaded on the 33rd floor, sources told ABC.

NFL employees were told to shelter in place, ESPN’s Jeff Darlington reported. The NFL is located on floors five through eight.

ABC News reported the officer was taken to Weill Cornell Medical Center in Manhattan where he was pronounced dead. At least one of the civilians was brought to Bellevue Hospital.

The Fire Department of New York said emergency crews were called to the Park Avenue office building Monday evening for a report of someone shot. A spokesperson said the call came in around 6:30 p.m. but provided no other details.

Mayor Eric Adams said multiple people were injured. He posted a clip to social media urging people still inside the office building to stay put because police officers were conducting a floor-by-floor search. The mayor said he was headed to the hospital to speak with the families and loved ones of those involved.

Local TV footage showed lines of people evacuating the office building with their hands above their heads. The building includes offices of Blackstone and the consulate general of Ireland.

Jessica Chen told ABC News she was watching a presentation with dozens of other people on the second floor when she “heard multiple shots go off in quick succession from the first floor.”

She and others ran into a conference room and barricaded tables against the door.

“We were honestly really, really scared,” she said, adding that she texted her parents to tell them that she loves them.

The building where the shooting happened is in a busy area of midtown, located a short walk north from Grand Central Terminal and about a block east of St. Patrick’s Cathedral.

The city’s emergency management alert system warned of traffic delays, road closures and disruptions to public transportation in the area.

Information from The Associated Press was used in this report