A father who was a serving police officer is among four people who were killed in a shooting attack at an office building in a busy district of New York City.

Didarul Islam, 36, was shot dead while providing security for the site on Park Avenue. Officials said he had migrated to the US from Bangladesh, had two children and was expecting a third with his pregnant wife. He died "a hero", they said.

Paying tribute to the late officer, New York Mayor Eric Adams said he was "doing what he does best... saving lives. He was protecting New Yorkers".

Three civilians, two male and one female, were also killed, Adams said. Details about them have not been made public. Another man is in a critical condition.

Suspected lone gunman Shane Tamura, a 27-year-old from Nevada, also died from a self-inflicted gunshot wound, officials said.

He had a "documented mental health history", and his potential motive is unknown.

Tamura is believed to have shot Islam dead first as he entered the skyscraper at 345 Park Avenue. He went on to attack others, ascending to the building's 33rd floor before turning his gun on himself.