Survivors, police and firefighters gave the same account of a band member setting the ceiling's soundproofing ablaze, he said.
"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 AP.
"The toxic smoke made people lose their sense of direction so they were unable to find their way to the exit. At least 50 bodies were found inside a bathroom. Apparently they confused the bathroom door with the exit door."
In the hospital, the doctor "saw desperate friends and relatives walking and running down the corridors looking for information," he said, calling it "one of the saddest scenes I have ever witnessed."
Rodrigo Moura, identified by the newspaper Diario de Santa Maria as a security guard at the club, said it was at its maximum capacity of between 1,000 and 2,000, and partygoers were pushing and shoving to escape.
Santa Maria Mayor Cezar Schirmer declared a 30-day mourning period, and Tarso Genro, the governor of the southern state of Rio Grande do Sul, said officials were investigating the cause of the disaster.
The blaze was the deadliest in Brazil since at least 1961, when a fire that swept through a circus killed 503 people in Niteroi, Rio de Janeiro.
