Hours later, the horrific chaos had transformed into a scene of tragic order, with row upon row of polished caskets of the dead lined up in the community gymnasium in the university city of Santa Maria. Many of the victims were under 20 years old, including some minors.
The first funerals of victims were planned for Monday.
As the city in southern Brazil prepared to bury the 233 people killed in the conflagration caused by a band's pyrotechnic display, an early investigation into the tragedy revealed that security guards briefly prevented partygoers from leaving through the sole exit. And the bodies later heaped inside that doorway slowed firefighters trying to get in.
"It was terrible inside - it was like one of those films of the Holocaust, bodies piled atop one another," said police inspector Sandro Meinerz. "We had to use trucks to remove them. It took about six hours to take the bodies away."
Survivors and another police inspector, Marcelo Arigony, said security guards briefly tried to block people from exiting the club. Brazilian bars routinely make patrons pay their entire tab at the end of the night before they are allowed to leave.
"It was chaotic and it doesn't seem to have been done in bad faith because several security guards also died," he told The Associated Press.
Later, firefighters responding to the blaze initially had trouble entering the club because "there was a barrier of bodies blocking the entrance," Guido Pedroso Melo, commander of the city's fire department, told the O Globo newspaper.
Police inspectors said they think the source of the blaze was a band's small pyrotechnics show. The fire broke out sometime before 3 a.m. Sunday and the fast-moving fire and toxic smoke created by burning foam sound insulation material on the ceiling engulfed the club within seconds.
Authorities said band members who were on the stage when the fire broke out later talked with police and confirmed they used pyrotechnics during their show.
Meinerz, who coordinated the investigation at the nightclub, said one band member died after escaping because he returned inside the burning building to save his accordion. The other band members escaped alive because they were the first to notice the fire.
The fire spread so fast inside the packed club that firefighters and ambulances could do little to stop it, survivor Luana Santos Silva told the Globo TV network.
"There was so much smoke and fire, it was complete panic, and it took a long time for people to get out, there were so many dead," she said.
Most victims died from smoke inhalation rather than burns. Many of the dead, about equally split between young men and women, were also found in the club's two bathrooms, where they fled apparently because the blinding smoke caused them to believe the doors were exits.
There were questions about the club's operating license. Police said it was in the process of being renewed, but it was not clear if it was illegal for the business to be open. A single entrance area about the size of five door spaces was used both as an entrance and an exit.
Family members of those killed walked around the gym in a daze Sunday evening, shuffling between caskets or holding one another and weeping as they identified loved ones and tried to make sense of what had happened.
Elaine Marques Goncalves lost her son Deivis in the fire. Another son who attended the college party at the nightclub, Gustavo, was barely alive after suffering two cardiac arrests caused by smoke inhalation.
She learned of the blaze after the mother of her sons' friends called her early Sunday.
"My boys were not home and I had no news. I turned on the TV - the tragedy was all over the television," she said at the makeshift morgue. "All I knew was they had gone to a club, I didn't know which one. I kept saying: 'Where do I start? Where do I go?'"
Television images from the city of about 260,000 people showed black smoke billowing out of the nightclub as shirtless young men who attended a university party there joined firefighters using axes and sledgehammers to pound at the hot-pink exterior walls, trying to reach those trapped inside.
Bodies of the dead and injured were strewn in the street and panicked screams filled the air as medics tried to help. There was little to be done; officials said most of those who died were suffocated by smoke within minutes.
Within hours the community gym was a horror scene, with body after body lined up on the floor, partially covered with black plastic as family members identified kin.
Outside the gym police held up personal objects - a black purse, a blue high-heeled shoe - as people seeking information on loved ones crowded around, hoping not to recognize anything being shown them.
The gathering was a party organized by students from several academic departments from the Federal University of Santa Maria. Such organized university parties are common throughout Brazil.
Survivor Michele Pereira told the Folha de S. Paulo newspaper that she was near the stage when members of the band lit some sort of flare.
"The band that was onstage began to use flares and, suddenly, they stopped the show and pointed them upward," she said. "At that point, the ceiling caught fire. It was really weak, but in a matter of seconds it spread."
Guitarist Rodrigo Martins told Radio Gaucha that the band, Gurizada Fandangueira, started playing at 2:15 a.m. "and we had played around five songs when I looked up and noticed the roof was burning."
"It might have happened because of the Sputnik, the machine we use to create a luminous effect with sparks. It's harmless, we never had any trouble with it," he said. "When the fire started, a guard passed us a fire extinguisher, the singer tried to use it but it wasn't working."
He confirmed that accordion player Danilo Jacques, 28, died, while the five other members made it out safely.
Police Maj. Cleberson Braida Bastianello said by telephone that the toll had risen to 233 with the death of a hospitalized victim. He said earlier that the death toll was likely made worse because the nightclub appeared to have just one exit through which patrons could exit.
Federal Health Minister Alexandre Padhilha told a news conference that most of the 117 people treated in hospitals had been poisoned by gases they breathed during the fire. Only a few suffered serious burns, he said.
Most of the dead apparently were asphyxiated, according to Dr. Paulo Afonso Beltrame, a professor at the medical school of the Federal University of Santa Maria who went to the city's Caridade Hospital to help victims.
"Large amounts of toxic smoke quickly filled the room, and I would say that at least 90 percent of the victims died of asphyxiation," Beltrame told the AP.
Sunday's fire appeared to be the worst at a nightclub since December 2000, when a welding accident reportedly set off a fire at a club in Luoyang, China, killing 309.
Similar circumstances led to a 2003 nightclub fire that killed 100 people in the United States. Pyrotechnics used as a stage prop by the 1980s rock band Great White set ablaze cheap soundproofing foam on the walls and ceiling of a Rhode Island music venue.
Associated Press writers Marco Sibaja in Brasilia and Stan Lehman and Bradley Brooks in Sao Paulo contributed to this report.