(CNN) It was the eeriest of timing. The intro guitar riff had ended and country singer Jason Aldean had just stepped to the mic to belt out the first verse of his hit, "When She Says Baby."

At the same time, the rat-tat-tat of automatic gunfire filled the air

For a few seconds, no one seemed to react. His guitar strapped around his neck, Aldean sang the next line of the song -- about a woman helping him through bad days -- as dozens of gunshots, maybe as many as 50, peppered the crowd.

It wasn't until the third line -- "Some days I'd rather be a no show" -- that Aldean realized something frightening was happening. He stopped singing and darted to the back of the stage. The singer, his wife, his band and crew eventually fled to safety.

The crowd, some 22,000 people, gasped and looked around, confused but not yet in a state of full-blown panic. That would come shortly.

Thirty-two floors above them, behind the gilded windows of the Mandalay Bay hotel across the Las Vegas Strip, a 64-year-old man -- later identified as Stephen Paddock of Mesquite, Nevada -- was raining down bullets. By the time Paddock was dead, it was the deadliest mass shooting in modern US history.

From concern to chaos

Photos: Mass shooting at Las Vegas music festival Debris is scattered on the ground Monday, October 2, at the site of a country music festival held this past weekend in Las Vegas. Dozens of people were killed and hundreds were injured Sunday when a gunman opened fire on the crowd. Police said the gunman fired from the Mandalay Bay hotel, several hundred feet southwest of the concert grounds. It is the deadliest mass shooting in modern US history. Hide Caption 1 of 30 Photos: Mass shooting at Las Vegas music festival Broken windows of the Mandalay Bay are seen early in Las Vegas on Monday. Police said the gunman fired on the crowd from the 32nd floor of the hotel. Hide Caption 2 of 30 Photos: Mass shooting at Las Vegas music festival People cross a street near the Las Vegas Strip just after sunrise on Monday. Thousands were attending the music festival, Route 91 Harvest, when the shooting started. Hide Caption 3 of 30 Photos: Mass shooting at Las Vegas music festival People embrace outside the Thomas & Mack Center after the shooting. Hide Caption 4 of 30 Photos: Mass shooting at Las Vegas music festival Police arrive at the Sands Corporation plane hangar where some people ran to safety after the shooting. Hide Caption 5 of 30 Photos: Mass shooting at Las Vegas music festival A woman cries while hiding inside the Sands Corporation plane hangar. Hide Caption 6 of 30 Photos: Mass shooting at Las Vegas music festival Concertgoers dive over a fence to take cover from gunfire on Sunday night. Hide Caption 7 of 30 Photos: Mass shooting at Las Vegas music festival Police take position outside the Mandalay Bay. Hide Caption 8 of 30 Photos: Mass shooting at Las Vegas music festival A man lays on top of a woman as others flee the festival grounds. The woman reportedly got up from the scene. Hide Caption 9 of 30 Photos: Mass shooting at Las Vegas music festival Hide Caption 10 of 30 Photos: Mass shooting at Las Vegas music festival People are seen on the ground after the gunman opened fire. Hide Caption 11 of 30 Photos: Mass shooting at Las Vegas music festival People run from the festival grounds. Hide Caption 12 of 30 Photos: Mass shooting at Las Vegas music festival A woman is moved outside the Las Vegas Tropicana resort. Multiple victims were being transported to hospitals in the aftermath of the shooting. Hide Caption 13 of 30 Photos: Mass shooting at Las Vegas music festival People are searched by police at the Tropicana. Hide Caption 14 of 30 Photos: Mass shooting at Las Vegas music festival An ambulance leaves the intersection of Las Vegas Boulevard and Tropicana Avenue. Hide Caption 15 of 30 Photos: Mass shooting at Las Vegas music festival A man in a wheelchair is evacuated from the festival after gunfire was heard. Hide Caption 16 of 30 Photos: Mass shooting at Las Vegas music festival Victims of the shooting are tended to in the street. Hide Caption 17 of 30 Photos: Mass shooting at Las Vegas music festival Concertgoers help an injured person at the scene. Hide Caption 18 of 30 Photos: Mass shooting at Las Vegas music festival People gather around a victim outside the festival grounds. Hide Caption 19 of 30 Photos: Mass shooting at Las Vegas music festival A couple huddles after shots rang out at the festival. Hide Caption 20 of 30 Photos: Mass shooting at Las Vegas music festival An injured woman is helped at the Tropicana. Hide Caption 21 of 30 Photos: Mass shooting at Las Vegas music festival Police and emergency responders gather at the intersection of Las Vegas Boulevard and Tropicana Avenue. Hide Caption 22 of 30 Photos: Mass shooting at Las Vegas music festival A police officer takes position behind a truck. Hide Caption 23 of 30 Photos: Mass shooting at Las Vegas music festival A crowd takes cover at the festival grounds. Hide Caption 24 of 30 Photos: Mass shooting at Las Vegas music festival Police officers advise people to take cover in the wake of the shooting. Hide Caption 25 of 30 Photos: Mass shooting at Las Vegas music festival People tend to a victim at the festival grounds. Hide Caption 26 of 30 Photos: Mass shooting at Las Vegas music festival Police stand at the scene of the shooting. Hide Caption 27 of 30 Photos: Mass shooting at Las Vegas music festival A woman sits on a curb at the scene of the shooting. Hide Caption 28 of 30 Photos: Mass shooting at Las Vegas music festival Police are deployed to the scene. Hide Caption 29 of 30 Photos: Mass shooting at Las Vegas music festival A man makes a phone call as people run from the festival grounds. Hide Caption 30 of 30

Aldean was the headliner, the last act on the last day of the sold-out Route 91 Harvest country music festival. Many fans had been partying at the Las Vegas Village, a 15-acre greenspace outside the MGM Grand hotel, since early Sunday afternoon.

There were also children in the crowd, some of them propped up on their parents' shoulders.

Once Aldean's band stopped, the light show carried on for a few more seconds before cutting to black. Floodlights illuminated the crowd. Still not sure what to do, some concertgoers crouched while others made their way to the edge of the festival along the Strip.

Then came another, shorter volley of gunfire, and the evacuation grew more urgent. On cell phone footage, there are screams and expletives. People can be heard saying, "Don't push."

SiriusXM Country radio host Storme Warren, who was watching Aldean's performance from the side of the stage, said he at first thought the gunfire was fireworks. By the third barrage of gunfire, he realized "something was wrong" and took cover beneath the stage.

"The shells were hitting the deck of the stage when I was on it," he said.

Before Aldean's set, singer Jake Owen had performed. He was still on the stage when the gunfire began. As concern morphed into chaos, he said, people began darting for cover. He could see the "fear in everyone's eyes." Owen escaped to his nearby tour bus as the bullets came down.

"When the shooting started, it was ringing off the top of the stage. You could hear it hitting trailers, people scattering and it was chaos," Owen said.

"Next thing you know, it was just unloading," the country singer said, "like no doubt an automatic-sounding rifle or some sort of machine gun or something. And at that point is when you could tell the chaos and the fear in everyone's eyes and their demeanor was changed and everyone just started scrambling for any sort of cover."

As a second round of shots erupted, concertgoers near the stage flattened on the grass, some using their bodies as shields to protect friends and loved ones. A few occasionally popped up like prairie dogs to see what was going on. Others yelled at them to "Get down!"

At the top of Carly Krygier's mind was her 4-year-old daughter. After the shooting started, she put her on the ground and covered the girl with her body. When there was a break in the gunfire, she ran to the bleachers, then to a hotel. Her daughter remained composed amid the ordeal, she said.

"She was amazing and so incredibly brave," she said.

'Dropping like flies'

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Taylor Benge, 21, said he was with his sister, who threw herself on top of him, telling him, "'I love you, Taylor. I love you.' And I'll never forget that," he said.

After they realized the bullets were coming from the direction of the Mandalay Bay, the two made their escape, but there were many obstacles, Benge said.

"Even hurdling over everything and getting over the fences and whatnot, it almost felt like we were getting closed in because no matter which direction you went in, no matter where you took cover, there was at least two to three bodies that were a part of it and you didn't know where you were safe," he said.

Corinne Lomas was one of those near the stage. She had blood on her legs from the bodies of injured people around her.

"People had to fall on top of each other, whether they were alive or not," she said. "I could see a guy with a bullet wound in his neck. ... People started dropping like flies."

Monique Dumas, who attended the show with her sister, said people in yellow shirts told the crowd, "Go! Go! Go! Go!" Before she fled, she saw someone on stage had been injured.

"The band was rushed off the stage, the floodlights came on the crowd and you see on the right hand of the stage the person who was injured. So they're calling for medics, calling for security, then there was gunfire again," Dumas said. "The gunfire never ended, it seemed like it went on and on and on."

First responders arrived, led by law enforcement carrying long rifles and wearing combat helmets. Many police officers took cover behind squad cars as they assessed the situation.

Amid the trampled grass littered with plastic beer cups and water bottles, concertgoers in cowboy hats huddled together, looking for a place to hide. Others peered out from behind stanchions as mayhem spilled onto the Strip and into nearby hotels.

Mad rush to safety

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Videos from the scene show people performing first aid on a sidewalk, women weeping on the curb, shirtless men in blue jeans helping people to safety and a man being ferried away in a wheelchair.

In one image, frantic concertgoers carry a wounded woman by her ankles and elbows into the Tropicana Hotel, one of the many nearby hotels where frightened people sought refuge.

Red crowd-control fences around the venue were toppled as concertgoers fled. Some people repurposed them as gurneys, using them to carrying the injured to safety.

One witness told CNN affiliate KLAS there was more bedlam in the parking lot as scared concertgoers -- many separated from the rest of their parties -- hid beneath and behind cars.

"My husband and I ran out toward our car, and there were people hiding underneath my car for cover," said the woman, who didn't give her name. "And there was a gentleman who was shot and he said, 'Can you help me?' And so I put him in my car and I had like six people in my car, people without shoes, running, just to get away."

Bullets were "whizzing and just bouncing off the ground nearby," said photographer Brendon O'Neal , who was on the stage when the shooting began but quickly made his way to the parking lot, where he hid behind a police car.

"It felt like minutes that these heavy machine guns were just going on and wouldn't stop," he said. (It's not clear if Paddock was using machine guns; authorities have described guns found in his room as rifles.)

'Like shooting fish in a barrel'

Judging from the descriptions and audio from the scene, CNN law enforcement analyst James Gagliano said he suspects Paddock was using a "military-style weapon" with bullets being fed into the gun via a large drum or belt.

"He just had to point at the center (of the crowd) ... and squeeze the trigger," Gagliano said. "To use the analogy, it was like shooting fish in a barrel in that space."

CORRECTION: An earlier version of this story incorrectly spelled the name of country singer Jake Owen.