WASHINGTON — A ceremonial session of Congress to formally declare President-elect Joseph R. Biden Jr.’s victory devolved in an instant into a scene of violence and mayhem on Wednesday when a pro-Trump mob stormed the Capitol, halting the counting of electoral votes.
Journalists from The New York Times witnessed the events. Here is how the chaos unfolded.
Not long after Senator Mitch McConnell of Kentucky, the majority leader, warned his Republican colleagues that their efforts to overturn an American election would send its democracy into a “death spiral,” fear surged through the Senate chamber.
A large group of pro-Trump protesters broke through barricades and breached the building, and the police whisked Vice President Mike Pence off the dais and out of the chamber, as the shouts of the mob could be heard outside the door.
Above the Senate floor, inside the press gallery, reporters craned their necks to catch a glimpse of the havoc outside. Journalists were rushed into the Senate chamber, as staff aides shouted “In or out!” and scrambled to secure the doors against intruders. Senator Todd Young, Republican of Indiana, yelled for the doors to be locked.
Looking at her phone, Senator Amy Klobuchar, Democrat of Minnesota, alerted fellow senators to the escalating danger and called out that there had been “shots fired” somewhere in the melee. Panic tinged the voices of both lawmakers and journalists.
As it became clear the Senate chamber was not safe, security officers ordered the senators to leave.
As lawmakers and staff rushed out, aides snatched the boxes containing the Electoral College certificates, making sure that the vandals could not literally steal the results of the election.
“If our capable floor staff hadn’t grabbed them, they would have been burned by the mob,” said Senator Jeff Merkley, Democrat of Oregon.
Through the tunnels of the Capitol, senators walked quickly with an armed police escort. A member of Mr. McConnell’s security detail took the arm of the senator, who walks with a limp because of a childhood bout with polio, pulling and steadying him as they hustled away from danger.
Before long, the president’s supporters were inside the Senate chamber, prowling among the mahogany desks and even sitting on the marble dais where Mr. Pence had been seated not long before.
Across the Capitol, a police officer stepped onto the House rostrum to inform lawmakers that they might need to duck under their chairs.
“We now have individuals that have breached the Capitol building,” he told them, warning House members to be prepared to move quickly out of the chamber. “They are in the Rotunda.”
“Call Trump,” Representative Steve Cohen, Democrat of Tennessee, replied to shouts and grumbles from the House floor. “Call your friend.”
Representative Ruben Gallego, Democrat of Arizona and a veteran, jumped on the arm rests of chairs and began directing members, cautioning them to move calmly and quickly from the chamber.
Capitol Police officers passed out gas masks to reporters in the press area above, as lawmakers pulled their own silver-boxed masks from underneath the chairs in front of them. There were warnings that tear gas had been fired in the Capitol Rotunda, so they prepared to don the masks.
The chamber filled with frantic shouting and the whirring of the masks, their red lights flashing as lawmakers struggled to figure out how to unfold the plastic bags that were supposed to go over their heads. Police officers and members of the floor staff urged lawmakers to exit, clambering over chairs and banisters to reach the doors.
A wooden chest was pushed in front of the main doors to the chamber, through which Mr. Pence and the chests of election certifications had come just an hour earlier. Security officers drew their guns and pointed and yelled at the door, whose glass panels were shattered, as lawmakers, staff aides and reporters cowered in the top levels of the chamber.
There was a bang, and evacuation momentarily stopped. Everyone was told to get down, with reporters and lawmakers struggling to hide behind low-backed chairs and equipment normally used to broadcast the floor proceedings.
Outside, members of the mob were making themselves at home throughout the Capitol, including inside Speaker Nancy Pelosi’s office.
Shortly after 2:45 p.m., the evacuation resumed, with a line of lawmakers and journalists clambering out of the House chamber. They were climbing over chairs, ducking under banisters — anything to get out quickly. Police officers had their guns drawn.
“Are you OK? Are you OK?” was the constant refrain as the members of Congress, aides and reporters scurried down staircases and hallways. Phones buzzed with texts and calls, with lawmakers frantically checking on staff aides who had been in office buildings and responding to family.
Senators gathered at a secure location in another building in the Capitol complex, with journalists asked to stay outside. F.B.I. tactical units in camouflage with firearms and shields monitored the location, as senators spoke in hushed tones about whether and how to proceed with the electoral count.
“These thugs are not running us off,” said Senator Joe Manchin III, Democrat of West Virginia. “We’re going to finish tonight. Everyone is committed to staying whatever it takes to get our job done.”
As night fell, an announcement came over the loudspeaker in the Capitol telling lawmakers the city was now under a curfew. Distant sirens could still be heard blaring throughout the capital.
Nicholas Fandos contributed reporting.