Sources: 3 killed at NYC building housing NFL HQ

A gunman opened fire Monday outside a midtown Manhattan office building that houses the National Football League and some of the country's top financial firms, killing an off-duty police officer working security in the building and two others, sources told ABC News.

Police believe the suspect later died from a self-inflicted gunshot wound after fleeing into the 44-floor-high building, located at 345 Park Avenue, sources told ABC. 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 barricading himself on the 33rd floor of the building, police sources said.

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

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 mayort said he's headed to the hospital to speak with the family 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.

Some finance workers at an office building down the block were picking up dinner at a corner eatery when they heard a loud noise and saw people running.

"It was like a crowd panic," said Anna Smith, who joined the workers pouring back into the finance office building. They remained there for about two hours before being told they could leave.

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