The shooter, who has been identified as 31-year-old teacher Cole Allen, of California, got past two security checkpoints at the venue before he was brought down.
He was armed with a shotgun, a handgun, and multiple knives, according to police.
An investigation into the attempted shooting will probably focus on how the suspect was able to smuggle a shotgun into the hotel.
Attendees noted that a magnetometer had been placed outside the ballroom, but that there was no screening when entering the hotel itself.
Why the King will not be fazed by attack on Trump
By Hannah Furness, Royal Editor
In 1994, when the King, then the Prince of Wales, was shot at while on stage in Australia, his reaction was understated to say the least.
He readjusted his cufflinks, blinked a few times and watched on, slightly perturbed, as security bundled the gunman to the floor.
So it is safe to say the King will not be unduly concerned with news from the United States, where he will be landing on Monday, in the aftermath of the attempted shooting of its 47th president.
He’s brave,” said the president. “So he’s coming and we’re going to have a great time.”
Donald Trump was bundled from the room at the White House Correspondents’ Association dinner on Saturday night, in an attack that left one security agent injured and the press corps – dressed in their black tie as guests – sheltering under tables after they had been instructed to “get down”.
The security for the state visit, which is already unusually high compared to other countries, will be at its absolute maximum capacity.
The opportunities for walkabouts are limited compared to royal visits in Britain, although the Palace has insisted on moments for the King and Queen to meet the public, as they always do on overseas tours.
Nerves behind the scenes have already been tested, if not quite frayed.