At least 58 people were killed and 515 were injured in Las Vegas Sunday night when a gunman opened fire on a music festival crowd from the 32nd floor of the Mandalay Bay Resort and Casino. It was the deadliest shooting in modern U.S. history.

The "nonstop gunfire," according to one witness, sent more than 22,000 country music fans scrambling for their lives. Two sources familiar with the investigation said there was a combination of rifles and handguns at the scene, and one of the sources said there were 19 weapons in the room.

Terrified bystanders ducked, ran and then sprang into action, frantically caring for the wounded. As ambulances rushed to the scene, concertgoers who had just been enjoying the final night of the Route 91 Harvest Music Festival, which was taking place across the street from Mandalay Bay, made makeshift stretchers out of police barricades.

They plugged wounds with their bare hands and used their clothing to try to stanch each other's bleeding. At least one man described a stranger who died in his arms.

An off-duty Las Vegas police officer who was attending the concert was among the dead, police said.

Jason Aldean was the headliner of Sunday night's concert; video showed his rushing off the stage amid the gunfire. Other performers from this weekend included country stars Jake Owen, Big & Rich, Luke Combs and Dylan Scott.

Las Vegas shooting death toll rises to 58, no apparent connection to terror

Good Morning America KARMA ALLEN and EMILY SHAPIRO,Good Morning America 1 minute 3 seconds ago

At least 58 people were killed and 515 were injured in Las Vegas Sunday night when a gunman opened fire on a music festival crowd from the 32nd floor of the Mandalay Bay Resort and Casino. It was the deadliest shooting in modern U.S. history.

The "nonstop gunfire," according to one witness, sent more than 22,000 country music fans scrambling for their lives. Two sources familiar with the investigation said there was a combination of rifles and handguns at the scene, and one of the sources said there were 19 weapons in the room.

Terrified bystanders ducked, ran and then sprang into action, frantically caring for the wounded. As ambulances rushed to the scene, concertgoers who had just been enjoying the final night of the Route 91 Harvest Music Festival, which was taking place across the street from Mandalay Bay, made makeshift stretchers out of police barricades.

They plugged wounds with their bare hands and used their clothing to try to stanch each other's bleeding. At least one man described a stranger who died in his arms.

An off-duty Las Vegas police officer who was attending the concert was among the dead, police said.

Jason Aldean was the headliner of Sunday night's concert; video showed his rushing off the stage amid the gunfire. Other performers from this weekend included country stars Jake Owen, Big & Rich, Luke Combs and Dylan Scott.

In the wake of the shooting, the Las Vegas Police Department said authorities responded to a room on the 32nd floor of the Mandalay Bay hotel, where police said the suspected gunman, 64-year-old Stephen Paddock, was dead.

Police said they believe Paddock killed himself prior to police entry. Authorities believe the suspect used a device similar to a hammer to smash the hotel room windows.

The motive was unclear. “I can't get into the mind of a psychopath,” Sheriff Joseph Lombardo said at a news conference this morning.

Officials said this morning they have found no connection between the shooting and any international terrorist group. Officials added that the suspect was not known to law enforcement.

Authorities said the suspect checked into the hotel Thursday and that they are searching hours of surveillance video. Authorities said the suspect brought the guns in himself.

Police said Paddock, of Mesquite, Nevada, had no criminal history, save a minor citation. He appears to have worked as an accountant or auditor and was a licensed hunter and private pilot.

Videos filmed by onlookers gave a window into the chaos that ensued as the gunfire rang out, with some thinking that fireworks were going off.

Witness Brian Claypool said on "Good Morning America" that after the first round of gunfire, he ran into a little room that he described as a production area.

"The hardest for me was, I saw six young women. They were maybe 20, 22. They were all crying on the ground. I was trying to be calm," Claypool said, appearing emotional.

"But I thought at the moment of the Orlando shooting, because we were in this room," he said of the 2016 Pulse nightclub shooting that left 49 people dead. We didn’t know where the shooter was. We thought he was going to jump the fence and come in this room and shoot us all. ... I’m thinking, 'Am I going to die in this room?'"

"Then the shooting stopped," Claypool said, "And I peeked out the front of the door, I peek my head out, police officers scream, ‘Go! Go!’"

Claypool said he tried to bring comfort to the young women who were sheltering in the room with him.

"I said to myself, 'These girls aren’t going to die. I’m not going to die,” he said. “I need to get home to see my daughter. This is not happening.'"

Concertgoer Mike Cronk told ABC News that as Aldean was playing, it "kind of sounded like some fireworks going off. I think there was the first kind of volley, and then all of the sudden second volley. My buddy's like, 'I just got hit, you know.' He got hit three times. Then people started diving for the ground. And it just continued.

"It was pretty much chaotic," Cronk continued. "Lots of people got hit. ... It took a while to get him out. We had to get him over the fence and hiding under the stage for a while, you know, to be safe. And, finally, we had to move him because he had three chest wounds."

Cronk said his group finally tracked down an ambulance, "and basically the one guy ended up dying in my arms because he was bleeding," he said. "And my buddy got in there. We got three more people in the ambulance. ... But I just got a message from my buddy -- and he's going to be OK."

•Excerpted from a story by ABC News.

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