According to the reports I've seen, the club's capacity was about 1000 and there were nearly 2000 in the club at the time of the fire, so as Peter said, the club was at twice capacity. Very sad situation.
Update edit:
According to a more recent report, the nightclub's capacity was 690, and most police reports now estimate that there were about 1200-1300 in the club at the time of the fire.
According to this report: Brazil Nightclub Fire Prompts Inspections Brazil has temporarily closed 58 other local facilities that have had questionable fire inspections.