NEW YORK — Investigators on Sunday were searching for the cause of a fire that tore through a 50th-floor apartment at Trump Tower and killed a man inside.

Flames and thick, black smoke poured from windows of the president’s namesake skyscraper after the fire broke out Saturday evening.

Fire Commissioner Daniel Nigro said the apartment was ‘‘virtually entirely on fire’’ when firefighters arrived after 5:30 p.m.

‘‘It was a very difficult fire, as you can imagine,’’ Nigro told reporters outside the building in midtown Manhattan.

Todd Brassner, 67, who was in the apartment, was taken to a hospital and died a short time later, the New York Police Department said. Property records indicate Brassner was an art dealer who had purchased his unit in 1996. Officials said four firefighters also suffered minor injuries.

Shortly after news of the fire broke, President Trump, who was in Washington, tweeted: ‘‘Fire at Trump Tower is out. Very confined (well built building). Firemen (and women) did a great job. Thank you!’’ Asked if that assessment was accurate, Nigro said, ‘‘It’s a well-built building. The upper floors, the residence floors, are not sprinklered.’’

Fire sprinklers were not required in New York City high-rises when Trump Tower was completed in 1983.

Associated Press