LAS VEGAS -- Thousands of country music fans ran for cover as a gunman fired on them from a hotel on the Las Vegas Strip -- a mass shooting that is now the deadliest in modern US history.
At least 58 people were killed Sunday night when the shooter fired hundreds of bullets into the crowd, police said.
Another 515 people were hurt in the gunfire and ensuing stampede at the outdoor Jason Aldean concert.
Alexandria Cheplak called her father as she ran from the bullets.
"Everyone's dying around me," Jon Cheplak recalled her saying. "Everyone's dying. They shot my friend ... I've got to get out of here."
The gunman, identified as 64-year-old Stephen Paddock, unleashed a hail of bullets from the 32nd floor of the nearby Mandalay Bay Resort and Casino, Las Vegas Metropolitan Police Sheriff Joseph Lombardo said.
But why the massacre happened remains a mystery.
Latest developments
-- Police found 10 rifles inside Paddock's hotel room, Lombardo said. "We believe the individual killed himself prior to our entry," the sheriff said.
-- The gunman's brother tells CNN he was aware Paddock owned guns, but was not aware of any automatic weapons.
-- President Donald Trump says he will visit Las Vegas on Wednesday.
Festival turns into massacre
The massacre started around 10:08 p.m. Sunday (1:08 a.m. ET Monday) at the Route 91 Harvest festival, Lombardo said.
Taylor Benge was enjoying the concert with his sister when he heard a relentless onslaught of "200 to 300" bullets.
Benge lauded the heroics of his sister, who "threw herself on top of me and said, 'I love you, Taylor,'" he said.
"Even after an hour and 30 minutes, I didn't know if I was safe."
Witness Bryan Hopkins said he survived by jumping into a walk-in freezer at the Mandalay Bay hotel.
And country singer Jake Owen, who was on stage with Aldean, said children were among the crowd.
"I saw kids on their parents' shoulders tonight," he said. "This is something they'll never forget."
Las Vegas police officially issued a press release about the incident. You can read it here.
Police say that Paddock opened fire on a crowed of more than 22,000 concert-goers from his hotel room on the 32nd floor of the Mandalay Bay Hotel on Sunday evening around 10:00 p.m. Mountain Time.
When SWAT members responded to the call, they breached the hotel room and found the suspect dead. Police believe he killed himself just before they entered.
President Trump issued remarks on the shooting:
The investigation
Police said they believe Paddock acted alone. "Right now, we believe it's a sole actor, a lone-wolf-type actor," the sheriff said.
So far, the massacre has no known link to overseas terrorism or terror groups, a US official with knowledge of the case said.
And a woman who was described as a "person of interest" after the attack is now not believed to be involved in the shooting, police said in a statement.
"Marilou Danley is no longer being sought out as a person of interest," the Las Vegas Metropolitan Police Department said. "LVMPD detectives have made contact with her and do not believe she is involved with the shooting on the strip."
The gunman's brother, Eric Paddock, said he was stunned to learn Stephen was responsible for the deadliest mass shooting in modern US history.
"He was my brother, and it's like an asteroid fell out of the sky," Eric Paddock told CNN outside his home in Orlando, Florida.
The last time he spoke to his brother was when Stephen texted him, asking how their mother was doing after losing power from Hurricane Irma.
Eric Paddock said he knew his brother owned a few handguns and maybe one long rifle, but said he did not know of any automatic weapons.
MGM Mandalay Bay Resort issued a statement via twitter about the shooting:
WARNING: Video is graphic and may be disturbing to some.
Police have issued a phone number for those who are searching for loved ones following the massacre:
'Beyond horrific.' Country music world stunned by Las Vegas shooting
Aldean, who was the headliner on the final night of the festival, was able to take shelter. A representative for Aldean confirmed that "he, his band and crew are all unharmed."
The country music community expressed shock and disbelief at the shooting.
Jake Owen, who performed right before Aldean, tweeted that he witnessed "the most unimaginable event."
"Gun shots were ringing off of the stage rigging and road cases" by the stage, Owen wrote. "No one knew where to go..thank you LVPD and responders for keeping us safe."
Brad Paisley, who performed at the festival last year, tweeted: "Praying for everyone at #HarvestFestival. There are no words right now that suffice."
Martina McBride, who was also there last year, wrote that she was watching the news coverage of the shooting early Monday morning and "praying for everyone's safety."
A few hours after the attack, Aldean posted a "Pray for Las Vegas" message on Instagram. "Tonight has been beyond horrific," he wrote.
"It hurts my heart that this would happen to anyone who was just coming out to enjoy what should have been a fun night."
Aldean's wife Brittany, who was also at the festival, posted a similar message calling for prayers.
"We are safe... our angels were definitely watching over us tonight," she wrote. "No words for what happened... Just horrific. Praying for everyone."
The Route 91 Harvest Festival is hosted by the events company LiveNation. It has been held each year since 2014.
The festival had multiple stages at Las Vegas Village, an open-air setting that is diagonally across the street from the Mandalay Bay hotel complex. The shooter reportedly fired from a high floor in the hotel.
Singer Kane Brown, who performed at the festival earlier in the day, wrote on Twitter immediately after the shooting, "This world is sick."
Aldean's performance at the festival came toward the end of a months-long tour.
'Go, go, go, go'
Derkef's sister, Monique Dumas, said that everyone instantly crouched when they heard the shots.
"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.
"It seemed there was a pause in the gunfire and the people in the yellow shirts were telling the people to 'go, go, go, go' ... the gunfire never ended, it seemed like it went on and on and on," she said.
SiriusXM Country radio host Storme Warren was on the side of the stage as Aldean was performing and shots rang out.
"I thought it was fireworks going off and maybe it mistriggered, and then it happened again. And when it happened the third time, we knew something was wrong," Warren said. "To say that I saw things I never want to see again is the truth, and it's a scary situation."
Warren said he heard "more than 50 shots fired and probably in the hundreds."
"The shells were hitting the deck of the stage when I was on it," he said, adding that he could still hear the shells as he went under the stage for protection.
A concertgoer told CNN affiliate KLAS that everybody was lying on top of each other trying to get out of the shooter's way.
"Everybody's hiding everywhere, they're hiding under the bleachers and the stanchions, anywhere they could and everyone is telling us to 'run, run as fast as you can,'" she told the news station. "And my husband and I ran out toward our car and there were people hiding underneath my car for cover 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."
'Sounded like firecrackers'
Eyewitness Bryan Heifner spoke to CNN from a room in a hotel across from the Mandalay Bay, which he said he could see from his window.
"Mostly I heard the shots, just so many shots -- I just thought it was a semi braking with the air brakes, but then I went downstairs and saw people running and looking for family," he said.
"I immediately went back to my room, locked the door, turned the lights off."
Another witness told CNN affiliate KSNV that the shooting sounded like firecrackers at first.
"It didn't sound normal, it sounded like machine guns and it was like several rounds, it was like hundreds of rounds," she told the news station.
"My boyfriend had me move behind a building here because it just didn't sound right," she told KSNV. "And then we hid behind a building and we could just hear hundreds of rounds going off and then about 10 minutes later the police came and just blocked off all the streets."
She said she was about a block from the Harvest 91 Festival.
Facebook has set up a crisis response page to help people establish whether their loved ones are safe.
Blood donations needed
With hundreds of victims still hospitalized, officials feared the death toll will keep rising.
The sheriff implored the community to donate blood. And before dawn, throngs of donors had already lined up outside a blood bank.
Shanda Maloney tweeted a photo while she stood in line at 4:30 a.m.
"This. Is. Vegas. This is our community. These are our people. Thank you to everyone here donating," she tweeted.
Maloney told CNN she also gave transportation to anyone who needed it after the attack.
"I just started picking people up and giving people rides," she says.
Nevada Gov. Brian Sandoval said on Twitter that a "tragic & heinous act of violence has shaken the #Nevada family" and offered prayers to all those affected by "this act of cowardice."
'We just ran for our lives'
Rachel De Kerf filmed her escape from the venue using her cell phone, starting just after the first shots were fired.
She described ongoing gunfire, and played out the video she had recorded during which more than five minutes of gunfire were intermittently audible.
"The gunshots lasted for 10-15 minutes. It didn't stop," she said. "We just ran for our lives."
De Kerf's sister, Monique Dumas, said that everyone instantly crouched when they heard the shots.
"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.
'Go, go, go'
SiriusXM Country radio host Storme Warren was on the side of the stage as Aldean was performing when the shots rang out.
"I thought it was fireworks going off and maybe it mistriggered, and then it happened again. And when it happened the third time, we knew something was wrong," Warren said.
"The shells were hitting the deck of the stage when I was on it," he said, adding that he could still hear the shells as he went under the stage for protection.
"It seemed there was a pause in the gunfire and the people in the yellow shirts were telling the people to 'go, go, go, go' ... the gunfire never ended, it seemed like it went on and on and on," Dumas said.
A concertgoer told CNN affiliate KLAS that everybody was lying on top of each other trying to get out of the shooter's way.
"My husband and I ran out toward our car, and there were people hiding underneath my car for cover," she said.
"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."
'Like shooting fish in a barrel'
Audio of the shooting suggested that the shooter had used a military-style weapon, CNN law enforcement analyst James Gagliano said.
"Automatic weapon(s) like that -- had to be numbers of magazines or a very large drum, it sounded to me like a belt-fed weapon, a military-style weapon and then to be shooting down, to use the analogy, it was like shooting fish in a barrel in that space," Gagliano said.
MGM Resorts, which owns the Mandalay Bay, tweeted its condolences.
"Law enforcement and emergency personnel responded quickly to the incident a secured the scene," it said in a statement. "Law enforcement requested that we put hotels in the vicinity on lockdown to ensure guest safety. We will provide more information as it becomes available."