It was toward the end of the night at Pulse, a gay nightclub in Orlando, Florida, when club-goer Christopher Hansen had taken his first sip from a drink and heard sharp noises ringing out in succession. He thought it was a beat of the song pulsating in the venue until people started crumpling onto the dance floor.
"I just saw bodies going down. Bang, bang, bang," he recalled to NBC News.
The club was packed with more than 300 people for Latin night about 2 a.m. ET Sunday. Hansen said he didn't see the gunman — later identified as 29-year-old Omar Mateen — but his first instinct was to get down and crawl away from the center of the shooting as 20 or 30 shots rung out.
"People stomped on me. ... I was zigzagging just in case, because you could still hear the bullets going off," he said. "I was terrified. I was in shock."
He was already near the exit when he crawled past the bathroom and made it outside to relative safety. There were people bleeding. A man who didn't speak English had a bullet in his back, and his pants were drenched in blood, Hansen said.
He tore off his bandanna and used it to suppress the bleeding.
"I had just seen the movie 'The Conjuring 2'" before going to the club, Hansen added. "To go from a horror movie to a real horror, it's just shocking."
Police say Mateen killed at least 50 people and injured 53 others in what's being described as the worst mass shooting in U.S. history.
A motive was still under investigation, although his family told NBC News he may have carried out the carnage after seeing two men kissing in Miami while with his wife and young son. Law enforcement sources told NBC News that Mateen had called 911 before the shooting to pledge allegiance to ISIS's leader, Abu Bakr al-Baghdadi.
About 5 a.m., authorities sent in a SWAT team to rescue club-goers who were being held hostage.
Mateen, who officials say was carrying an AR-15-type rifle with large-capacity magazines, was killed.
Joshua McGill said he and his roommates hid in an employee area of the club before rushing outside.
"During my run across the parking lot, I did hear more shooting, and I ducked behind a car and crawled under the car," McGill, a nursing student, told NBC News. "That's when I noticed another club-goer staggering, covered in blood, and I helped him get behind the car."
Jackie Smith, who was also inside the club, said two friends next to her were shot.
"Some guy walked in and started shooting everybody. He had an automatic rifle, so nobody stood a chance," Smith told The Associated Press. "I just tried to get out of there."
Relatives and friends, many in tears, gathered outside hospitals to learn whether their loved ones were among the dead or wounded.
Smith did not know the conditions of her friends and came out of the hospital and burst into tears.
The wounded included one police officer who was shot and suffered injuries to his face, officials said.
Jon Alamo said he was at the back of one of the club's rooms when a man holding a weapon came into the front of the room.
"I heard 20, 40, 50 shots," Alamo said. "The music stopped."
Club-goer Rob Rick said the shooting started just before closing time.
"Everybody was drinking their last sip," he said.
He estimated that more than 100 people were still inside when he heard shots, got on the ground and crawled toward a DJ's booth. A bouncer knocked down a partition between the club area and an area in the back where only workers are allowed — so people inside were able to then escape through the back of the club.
Hansen said he moved to the Orlando area about two months ago and was expecting only to have fun — not to see the night descend into chaos.
"There's sweat and blood, I know it's under my nails," he said. "This is just a tragic situation."