Four people, including an off-duty NYPD officer, were killed in a mass shooting inside a busy Manhattan skyscraper in the heart of midtown early Monday evening, city and police officials said.

The dead include Didarul Islam, 36, an off-duty officer and father of two who was working security in the building, and three civilians — two males and one woman.

The lone gunman also took his own life on the building's 33rd floor, shooting himself in the chest, officials said.

Another individual was shot and is in critical but stable condition, Mayor Eric Adams said in a news conference on Monday night at NewYork-Presbyterian/Weill Cornell Medical Center.

"He was saving lives," Adams said of Islam, a 3½-year veteran of the force. "He was protecting New Yorkers. He's an immigrant from Bangladesh.

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