A man armed with knives, a shotgun and a handgun was barreling through security at a full sprint, heading toward the ballroom at the Washington Hilton.

At that moment on Saturday night, President Trump and many of America’s top government officials and journalists were one floor down, crammed into the ballroom for a black-tie dinner. The mentalist Oz Pearlman, the night’s entertainer, was leaning over Mr. Trump and the first lady, demonstrating one of his mind-reading tricks by trying to guess the name that the White House press secretary had picked out for her baby, due to be born any day.

Suddenly, the look on Mr. Pearlman’s face changed to one of alarm. Several loud but strangely muffled bangs were going off somewhere in the distance. The first lady ducked under the table. The president stayed seated as Secret Service agents, dressed in tuxedos, surrounded him and began to draw their weapons.

The pop-pop-pop that the crowd was hearing was the sound of gunfire before the authorities managed to tackle the suspect, who never made it into the ballroom. But in the moment, it was difficult to tell what exactly was happening. Guests dived to the floor and hid behind chairs. Secret Service agents climbed over tables to protect cabinet members and some of the country’s most high-ranking officials, smashing plates of spring peas and burrata that had been served only minutes earlier.

As agents hustled the president out of the room, Mr. Trump appeared to trip or get pushed down. Vice President JD Vance was pulled from his seat by his shoulders. When agents grabbed Tulsi Gabbard, the director of national intelligence, they briefly got stuck between two tight tables and had to redirect toward a different exit.

The suspect, identified as Cole Tomas Allen, 31, of Torrance, Calif., was taken into custody quickly. And while the investigation is in its early stages, Todd Blanche, the acting attorney general, said Mr. Trump was “likely” a target, along with others in the administration.

It was a shocking night. And in that way, it was in keeping with the nonstop, previously unimaginable events of Washington in the Trump era, in which no week seems to pass by without some extraordinary turn of events. By the end of the evening, the president would show graciousness to the journalists he had planned to skewer and, after 15 months of attacking Democrats and reporters as enemies, he would take the occasion to call for unity.

Mr. Trump rushed back to the White House to speak to the nation about what he had just been through, suggesting that only the most consequential leaders become targets of assassins and using the moment to sell the need for his beloved White House ballroom. Reporters, editors and influencers on the scene scrambled for cover, but not without holding their phones aloft for livestreams, Instagram posts and documentation of a crime in progress.

Some of them made it out to after-parties scattered all over town, but the gatherings were scaled back or half empty, since many reporters ended up working late into the evening.

This account of the pandemonium that erupted on Saturday night at the White House correspondents’ dinner is based on reporting by New York Times journalists who were on the scene, surveillance footage and interviews with other witnesses.

‘Shots Fired!’

Even before the chaos broke out, Saturday was expected to be an intense spectacle. Just not like this.

It was Mr. Trump’s first time attending this black-tie dinner as president. He would be showing up to make remarks after a year spent sparring with reporters who cover him, suing them and their employers for billions of dollars and insulting them, often in viciously personal terms.

As he pulled out of the White House driveway a few minutes before 8 p.m., he could be seen looking over a printed copy of the speech he planned to give that evening — one he would later characterize as the “most inappropriate speech ever made.”

No one would get to hear it.

Inside the cavernous ballroom, guests were seated at tables of 10. Waiters, squeezing through the packed room of more than 230 tables, made the rounds to pass out bottles of champagne.

Most of Mr. Trump’s cabinet and top officials were in attendance. Kash Patel, the F.B.I. director, was seated toward the back of the room with The Daily Mail. Treasury Secretary Scott Bessent and Lee Zeldin, the Environmental Protection Agency administrator, were closer to the front.

The main course had not even been served by the time the gunshots were heard.

Gun-toting agents started running through the hallways outside the ballroom, screaming at people to get low. Caterers in white jackets cried out in terror as they bolted for cover in a stairwell. The gunfire sounded like shattering plates; the president would later say he thought it was a tray clanging to the floor.

“Shots fired, shots fired!” agents called out as they pinioned the small group of reporters and photographers traveling with the president into a corner against a wall.

A moment later, various cabinet members with heavy security details were escorted out of the ballroom with stricken looks on their faces. Health Secretary Robert F. Kennedy Jr. and his wife, Cheryl Hines, appeared around the corner first; guards were gripping Mr. Kennedy so tightly that he appeared to be limping. Bystanders worried he had been shot. His guards stood him up a little straighter as they began banging their fists on an elevator door to open.

Jeanine Pirro, the U.S. attorney for the District of Columbia, came wheeling around the corner and into a different elevator. Mr. Patel tore down the hallway with two men in tow.

Inside the ballroom, as guests took shelter under tables and behind chairs, Michael Glantz, a top agent at Creative Artists Agency, stayed in his seat and picked at the burrata on his plate — a stark contrast to the chaotic scene unfolding and one that was captured live on CNN and went viral on social media.

On Sunday, Mr. Glantz said he did not consider leaving his seat.

“First of all, I have a bad back,” he said. “I couldn’t get on the floor, and if I did get on the floor, they’d have to bring in people to get me off the floor. And No. 2, I’m a hygiene freak. There was no freaking way I was getting in my new tux on the dirty Hilton floor. It was not happening.”

‘Let the Show Go On’

Shortly after Mr. Trump was whisked offstage, he made clear that he wanted the dinner to proceed.

“Quite an evening in D.C.” Mr. Trump wrote on Truth Social at 9:17 p.m. “Secret Service and Law Enforcement did a fantastic job. They acted quickly and bravely. The shooter has been apprehended, and I have recommended that we ‘LET THE SHOW GO ON’ but, will entirely be guided by Law Enforcement.”

Hotel staff reset the place settings at the head table and refilled the cups with water and ice. Weijia Jiang, a CBS News correspondent and president of the White House Correspondents’ Association, briefly returned to the stage and said the dinner would begin again shortly.

“I know everyone is going to want as many details as possible, and right now we don’t have them,” Ms. Jiang said. “But I can tell you that our program is going to resume momentarily and we will have more details to share also momentarily.”

Security officials ultimately decided Mr. Trump had to leave, however. “Law Enforcement has requested that we leave the premises, consistent with protocol, which we will do, immediately,” the president posted on Truth Social at 9:36 p.m.

He also said he would be giving a news conference “in 30 minutes.”

The group of journalists that travels with the president wherever he goes — known as the press pool — was ushered back upstairs, out of the Hilton and into the waiting vans. The presidential motorcade peeled out of the parking lot at 9:45 p.m., racing down the hill back toward the White House.

Back at the White House, Secretary of State and National Security Adviser Marco Rubio was pacing outside on the driveway outside the West Wing in his tuxedo. He would soon be by the president’s side at a news conference that started just after 10:30 p.m.

‘It’s Always Shocking’

The 30-minute notice for a presidential news conference set off a mad dash among some journalists who struggled to find taxis with the hotel swarmed with law enforcement. Some decided to travel the mile and a half to the White House on foot, setting off at a quick trot.

The briefing room was filled with reporters in evening wear; the president, first lady and cabinet officials in attendance were also still in their formal clothes.

Mr. Trump updated the media on the situation — he said that a Secret Service officer had been shot but was protected by a bulletproof vest. He was taken to a hospital, officials said. There were no other reported injuries, according to Markwayne Mullin, the homeland security secretary.

“It’s always shocking when something like this happens,” Mr. Trump said, standing with the first lady, the vice president, the defense secretary, the secretary of state, the acting attorney general, the F.B.I. director and the press secretary.

He also used the moment to argue that his 90,000-square-foot ballroom project is necessary.

“I didn’t want to say this,” he said, “but this is why we have to have all of the attributes of what we’re planning at the White House. It’s actually a larger room, and it’s a much more secure. It’s got — it’s drone proof, it’s bulletproof glass.”

It’s not clear why the ballroom was entirely relevant; the dinner is staged by the White House Correspondents’ Association, a large collective of journalists, and not the administration. It has been held at the Hilton for more than five decades.

Still, Mr. Trump said he had spoken with the organizers of the correspondents’ dinner, and vowed to reschedule it within 30 days.

Michael M. Grynbaum contributed reporting.