Investigators on Sunday said the gunman who tried to storm a gala dinner attended by US President Donald Trump planned to target top government officials, as scrutiny grew over the event's security.

Trump, who was rushed out of the hotel ballroom in Washington by Secret Service agents, posted surveillance camera footage of the gunman attempting to sprint past a security checkpoint as guards drew their weapons.

After an exchange of gunfire, the suspect was detained at the scene and was being questioned Sunday before he is due to appear in court on Monday.

"He's not actively cooperating. I expect that he will be formally charged tomorrow morning in federal court in Washington," acting US Attorney General Todd Blanche said.

"We do believe, based upon just a very preliminary start to understanding what happened, that he was targeting members of the administration."

Blanche added no further motive was known for the attack, confirming the suspect -- who was armed with a shotgun, handgun and knives -- was staying at the Washington Hilton hotel where the black-tie dinner was held on Saturday evening.

"We believe that he traveled by train from Los Angeles to Chicago, and then from Chicago to Washington," Blanche said. "It appears he purchased these firearms in the past couple years."

Attendees dove under tables in chaotic scenes as Secret Service agents swarmed into the glitzy White House Correspondents' Association dinner, held annually in the US capital.

Trump said at a hastily arranged late-night news conference at the White House that he first thought the noise was a tray being dropped, before realising it was gunfire. He said he hoped the media gala would be rescheduled within a month.

"They seem to think he was a lone wolf, and I feel that too," Trump said. One officer was shot at close range in his safety vest and appeared to be not seriously harmed.

Multiple US news outlets identified him as 31-year-old Cole Tomas Allen from the southwestern Los Angeles suburb.

Trump was the target of an assassination attempt during a rally in Butler, Pennsylvania in 2024. A gunman fired several shots, killing an audience member and lightly wounding the president in the ear.

A few months later, another man was arrested after a Secret Service agent saw the barrel of a rifle poking from the bushes on the perimeter of the West Palm Beach golf course where Trump was playing a round.

The Washington Hilton where Saturday's gala was taking place was the site where Republican President Ronald Reagan was shot by a would-be assassin in 1981.

The incident late Saturday came less than 48 hours before King Charles III and Queen Camilla begin a four-day state visit to the United States. (AFP)


Edited by Priscilla Ng