The blaze in the southern city of Santa Maria was started when a band member or someone from its production team ignited a flare, which then set fire to the ceiling, said Luiza Sousa, a civil police official. The fire spread "in seconds," she said.
An estimated 500 people were in the Boate Kiss nightclub when the fire broke out early on Sunday, and many were unable to find the exits as dark smoke quickly filled the room. At least one exit was locked, trapping hundreds inside to die, many from asphyxiation as they inhaled smoke, police said.
"When I looked around, all I saw were dead bodies all around, lying on the floor. It was macabre," survivor Taynne Vendrusculo told GloboNews TV. "It all happened so fast. Both the panic and the fire spread rapidly, in seconds."
Television footage showed people sobbing outside the club, while shirtless firefighters used sledge hammers and axes to knock down an exterior wall to open up an exit.
By noon (1400 GMT), the death toll had risen to 245 and 48 people were being treated in local hospitals, said Major Cleberson Bastianello, head of the military police unit leading the rescue efforts. He said all of the bodies of the victims had been removed from the nightclub.
President Dilma Rousseff, who started her political career in the same state where the fire happened, cut short a visit to Chile to return to Brazil to visit the scene. Before departing, Rousseff gave a televised statement in which she broke out in tears as she pledged government help for the victims and their families.
"We are trying to mobilize all possible resources to help in the rescue efforts," she said. "All I can say at the moment is that my feelings are of deep sorrow."