ORLANDO (Florida) • Witnesses and club patrons said the shooting erupted at around 2am local time amid throbbing music as the crowded Pulse Nightclub was nearing closing time.
Speaking to Sky News, clubber Ricardo Negron, who was inside when the shooting began, described how the gunman raked the club with bullets.
"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.
He described hearing "non-stop firing" that probably lasted less than a minute, but felt a lot longer.
"There was a brief pause in the shooting and some of us just got up and ran out from the back," he said.
Witness Christopher Hanson told CNN he heard "loud banging noises, like gunshots going off".
SCENES OF HORROR
There were so many (shots)... It was constant, like 'pow, pow, pow'.
WITNESS JAVER ANTONETTI
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... There was a brief pause in the shooting and some of us just got up and ran out from the back.
WITNESS RICARDO NEGRON
We were dancing by the hip hop area when I heard shots - bam, bam, bam - and the only thing I could think of was to duck, but I ran out instead.
WITNESS JOEL FIGUEROA
I just saw bodies going down and I was ordering a drink at the bar. I fell down. I crawled out.
WITNESS CHRISTOPHER HANSON
People were trampling all over each other. I'm scared. I don't wanna go out.
MS JILLIAN AMADOR, who was discharged from hospital after being cut by glass during the attack.
I tend to think that the world is good. But when you get into a situation like this you go, 'what is going on?' This is not going to be easy to get through for a lot of people.
MS HELENE ROYSTER, mother of one of the witnesses.
Whether that is domestic terrorist activity or an international one, that is something we will certainly get to the bottom of.
MR DANNY BANKS, Florida Department of Law Enforcement special agent in charge.
"I didn't see any of the actual shooters. I just saw bodies going down and I was ordering a drink at the bar," he said.
"I fell down. I crawled out. People were trying to escape out the back. I just know that when I hit the ground, I was crawling and I hit my elbows and my knees."
There was "blood everywhere".
Mr Hanson, describing a man who had been shot, said: "I took my bandana off and shoved it in the hole in his back."
Ms Rosie Feba was at the club with a friend when the shooting broke out.
"She told me someone was shooting. Everyone was getting on the floor," she told the Orlando Sentinel. "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."
Police cars, ambulances and other emergency vehicles rushed to the scene, while streets around the club in South Orange Avenue were closed for several blocks.
On its Twitter feed, the Orlando Police Department asked residents to stay away from the area and said it was seeking support from state and federal agencies. Later, people who work in the area were asked to stay away if possible.
The club posted a message on its Facebook page at about 3am, saying: "Everyone get out of Pulse and keep running."
People streamed out of the club in chaos, with little idea of where to go. A crowd formed outside the club, looking for missing friends or family members. Some had rushed there after getting frantic calls from those trapped inside the club.
Local television networks also showed other people waiting anxiously outside hospitals, hoping to find out more about the whereabouts or condition of their loved ones.
One woman said she had rushed to the area after receiving a call from her daughter, who had said: "Please come get us, and come get us now."
Another mother told CNN: "A girlfriend of my son called and said he got shot. He got shot and she was crying."
She said she could not find her son, or even get information on where he had been taken.
Some of the victims had been transferred to other hospitals "because this hospital was full", the mother said outside Orlando Regional Medical Centre.
AGENCE FRANCE-PRESSE, NEW YORK TIMES