WASHINGTON (AFP) - It was a Saturday night at the Pulse nightclub, which could mean only one thing: a raucous, high-spirited celebration that would not end until the small hours.

Strobe lights were flashing and music blaring at the popular lounge, home to one of the hottest party scenes in Florida - and where 50 people died and 53 injured in the country's worst mass shooting.

Just a few days earlier, Orlando's vibrant LGBT community had marked the annual Gay Days celebration, one of the biggest events anywhere in the United States dedicated to gay pride.

The partying was to go on at Pulse, a club known for its drag shows and one of several gay-friendly establishments in downtown Orlando's vibrant after hours club scene.

"Tonight 21 and up is FREEEEEEEE before 11pm," Kenya Michaels, a well-known Puerto Rican drag queen who was slated to perform at the club, posted on Facebook earlier Saturday.

"Come see me show time at 12 am at Pulse Orlando Doors open at 9 pm. My sister Jasmine international is performing with me," posted Michaels - who escaped the shooting unharmed.

Scores of people turned out for the show: A contest of dancing, lip-synching drag queens took the floor one by one, showing their best dance moves, sashaying in high heels, as patrons laughed, nursed their cocktails, tossed dollar bills onto the stage.

One dancer with swiveling hips and a Beyonce-like mane slinked around podium, as video footage posted online on Periscope captured the revelry.

Crowd of patrons thronged the area just off-stage, raised bottles of alcoholic beverages and drank shots, amid a crescendo of laughter.

Then, at around 2am, with the party in full gear, barely discernible under the cheers and the throbbing music, were the sounds of what one reveller said sounded like drumbeats.

Patron Christopher Hanson said at first he thought the loud, rhythmic sounds were part of the pulsating music "until you heard too many shots. It was like, bang, bang, bang, bang."

At some point, it dawned on him that the "loud banging noises" were actually "gunshots going off", Hanson said.

"I didn't see any of the actual shooters," he told CNN.

"I just saw bodies going down and I was ordering a drink at the bar. I fell down. I crawled out. People were trying to escape out the back," he said.

"I just know that when I hit the ground, I was crawling and I hit my elbows and my knees. When I got across the street, there were people - blood everywhere."

The management of the Pulse club, grasping the gravity of the situation, quickly posted an emergency warning on its Facebook page.

"Everyone get out Pulse and keep running," it wrote.

The carnage was so unthinkable that patrons couldn't make sense of it, even as they watched their friends and loved ones falling all around them.

"Everyone was getting on the floor," said Rosie Feba, who was at the club with a friend when the shooting broke out.

"I told her I didn't think it was real, I thought it was just part of the music, until I saw fire coming out of his gun," she told the Orlando Sentinel.

One clubber, Ricardo Negron, described to Sky News how the gunman sprayed the ceiling of the club with bullets, as panicked patrons cowered in terror.

"People just dropped on the floor. I guess the shooter was shooting at the ceiling because you could see all the glass from the lamps falling," he told the network, describing "non-stop firing" which probably lasted less than a minute but felt like a lot longer.

"There was a brief pause in the shooting and some of us just got up and ran out the back," Negron said.

Other patrons said it seemed the shooting went on far longer - judging by the length of the song playing as the gunman raked the club with bullets.

Survivors - who just minutes earlier were dancing without a care in the world - suddenly were simply trying to escape with their lives.

Some told US media they were able to crawl out of the front of the establishment. Others ran out the back, while still others scrambled out of windows.

Many, however, did not make it out, including some who reportedly sought shelter in club's bathroom.

The shooting eventually became a hostage situation after the gunman barricaded himself in the club with scores of captive patrons.

The stand-off would not be resolved until more than three hours later, when police used an armored vehicle to ram down part of the building, eventually killing the gunman in a hail of bullets.

Tearful family members gathered outside of Pulse waiting for news of their loved ones, while others gathered at the hospital where the wounded club patrons had been taken.

One man told the Orlando Sentinel he sat with a victim, who had been shot in the back, shoving the bandana he had been wearing on his head into the man's bleeding wound to help staunch the flow of blood.

He was uncertain, when the ordeal was over, whether the man had survived.