Interior Minister Gabriel Oprea said yesterday the explosion occurred at a downtown club in the city of 3 million people.
Digi 24 television station cited witnesses who said the explosion came after a spark on a stage where a band was performing ignited some of the polystyrene decor.
Witnesses told Antena 3 TV there were between 300 to 400 young people at the club and there had been a "pyrotechnical show." The station reported that people panicked and rushed for the exit.
Some 50 people were taken to the Floreasca emergency hospital, the ministry said.