Attendees ducked under tables and took cover elsewhere in the hall amid the bedlam as multiple gunshots rang out.
One secret service operative was shot from close range, but was saved by his bulletproof vest, according to the president.
Hundreds remained in the ballroom for almost an hour until security cleared the hall.
The suspected shooter, who was reportedly wielding multiple weapons, is now in custody after he was apprehended on the scene “by very brave soldiers” of the secret service, Trump said.
Cole Tomas Allen, 31, of Torrance, California, has been identified as the suspect and he will be charged in court on Monday.
Allen was reportedly a guest at the hotel and worked as a part-time teacher in California.
Trump has posted a photo of the shooter on his Truth Social page.
In July 2024, Trump, who was campaigning for his second presidency, was rushed off the stage at a rally in Pennsylvania after a gunman fired a volley of shots into the crowd.
Trump was injured on one ear in that incident.