(CNN) When it was all over and the first of the responders made their way through the cavernous nightclub, feet gingerly stepping over the bloody bodies sprawled all around, they called out, "If you're alive, raise your hand."

Around them, the unanswered cell phones of victims chirped incessantly -- a soundtrack to a carnage, the likes of which America has never seen.

The attack at Pulse is the deadliest mass shooting in the United States.

It began early Sunday morning with two loud pops.

The gunshots lasted 'a whole song'

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Pulse bills itself as the "hottest gay nightclub in Orlando." But for the regulars there, it has always been more than that.

To many, it's a sanctuary. A place where they find comfort in community; where they seek haven from the hate that still lingers around them.

The club is known for its weekly themed performances, and Saturday night was Latin Night.

The 300 or so people who had crowded inside danced as the music pounded, the strobe lights flashed and shot boys served $5 skybombs.

Then as it neared the 2 a.m. closing time, Omar Mateen entered, with an assault rifle, a semiautomatic and allegiance to ISIS.

When the first two shots rang out, no one noticed. The sharp staccato almost went with the beat.

"I thought it was a Ying Yang Twins song or something," Christopher Hansen, who was inside, said.

It took a moment to sink in. For some, it was the flash from the gun. For others it was the unending booming reports - just one after another after another.

The gunshots went on for so long that the shooting "could have lasted a whole song," Hansen said.

Everyone 'keep running'

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People dove to the floor, trying to elbow-crawl for cover. Others lunged for the doors -- separating from friends, stepping over strangers.

"No one put two and two together until the fifth and sixth [shot]," said Luis Burbano, who had been at the bar. "Between 10 and 20, that's when everything really started getting real."

The loud music blaring from the speakers and the darkness of the dance floor compounded the confusion.

By 2:09 a.m., it was clear what was happening. The nightclub posted on its Facebook page: "Everyone get out of Pulse and keep running."

Luis Burbano and his best friend ran to an employee access door after they realized the gunshots were "getting closer and louder and louder."

He said he didn't turn back to look at the gunman.

"I didn't even want to look back. Why? To look at them, that'd be the last thing I would see, the last memory I have."

'God's got this'

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Ray Rivera, one of the Pulse DJs, was playing on the patio when he noticed everyone barreling out from the club.

Two people - a man and a woman -- dashed under his DJ booth to hide.

"The guy took off and the girl was down there panicking and I told her she needed to be quiet and as soon as there was a break in the shots, I pushed her and said, "Let's go.'"

Rivera and the woman bolted to safety.

Drenched in sweat and blood, club-goers who made it out safely tended to the wounded, forming tourniquets with their shirts.

Joshua McGill helped a victim, who was riddled with multiple gunshot wounds, limp to safety. He didn't know the man, but when they reached safety, they embraced each other.

McGill told him: "God's got this. You'll be OK."

'Answer your phone'

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But so many couldn't escape. For three harrowing hours, as the gunman took hostages, they crouched in a dressing room or in the air conditioning vents.

One person hid in the bathroom and said she survived by covering herself with bodies.

Helpless, trapped, shocked and scared, they texted their loved ones, pleading for help.

Eddie Jamoldroy Justice, a 30-year-old accountant, sought shelter in the bathroom from where he texted his mom:

Mommy I love you

In the club they shooting

Trapp in the bathroom

Call police

Im gonna die

His mother, Mina Justice, tried to reassure him that she'd called 911 and help was coming:

Calling them now.

U still there?

Answer your phone.

Call me.

Call me.

Justice replied: Call them mommy

Now

Im still in the bathroom

Hes coming

Im going to die

He then went silent. He was among the 49 who didn't make it.