LAS VEGAS — A gunman near the Mandalay Bay Casino started a rapid – fire bombardment during a huge outdoor concert festival on Sunday night, killing more than 50 people, injuring hundreds of others, and sending thousands of horrified survivors fleeing for cover, in one of the deadliest mass shootings in American history.

Singer Jason Aldean was performing outside at the Route 91 Harvest Festival, an online video showed. The three – day country music event, stopped when the sound of automatic gunfire had been heard. The music stopped, and as victims fell, bleeding, concertgoers screamed, ducked for cover, or ran.

Video of the shooting showed nine seconds of rapid – fire, continuous bursts, followed by 37 seconds of silence from the weapon amid panicked screaming. The bombardment of gunfire then erupted again in at least two more rounds.

“Get down,” one cried. “Stay down,” screamed another.

Also, video from the shooting showed Mr. Aldean, the final performer of the night, running off the stage as the gunfire erupted.

Sheriff Joseph Lombardo of the Las Vegas Metropolitan Police Department said on Monday morning that currently, the Clark County Fire Department is estimating the injuries to be well over 500.

He said there were about 22,000 people at the concert. One of those killed was an off – duty police officer, the department said.

The first reports of the shooting came at 10:08 p.m. local time. The sheriff identified the gunman to be Stephen Paddock, 64, of Mesquite, Nevada, who had no significant criminal history.

In the first hours after the shooting, the police searched for a woman described as “a companion” of the gunman, Marilou Danley. Later, the sheriff said she had been located out of the country, and apparently was not with Mr. Paddock when he checked into the hotel, but that “he was utilizing some of her identification.”

Before dawn on Monday, Mr. Lombardo said the police were executing a search permit on Mr. Paddock’s home, adding, “We’re going to clear the residence first for any possible explosives, so that will be slow and methodical.”

Eric Paddock, a brother of Stephen Paddock who lives in Orlando, Florida, told The Orlando Sentinel that he had made a statement to the police. “We are completely dumbfounded,” he said. “We can’t understand what happened.”

President Trump issued a statement on Twitter on Monday extending sympathies to the victims and their families and was scheduled to address the nation at 10:30 a.m. Eastern time.

Also, he said he would visit Las Vegas on Wednesday to meet with law enforcement, emergency medical workers, and families of victims.