Buenos Aires Health Secretary Alfredo Stern told local television on Friday that "the city does not remember such a terrible situation".
Local media reported that as many as 5000 to 6000 people may have been inside the club listening to a band play when the blaze broke out an hour just before midnight.
Witnesses said the fire started when a flare was shot into the club's ceiling, which was covered with foam. There was a stampede and many people fainted from inhaling smoke.
"There are versions that flares caused the fire, but I cannot confirm this until we have more information from the fire department," Mayor Anibal Ibarra said.
Police said the fire was extinguished quickly, but rescue workers continued to remove people on stretchers from inside the club. Television showed pictures of the bodies of young people lying on the sidewalks outside the club.
Parents rushed to the scene desperate to find their sons and daughters amid the chaos. Dozens of ambulances took the injured to 14 hospitals in the city.
The blaze was the worst in the Americas since a supermarket fire in neighbouring Paraguay last August killed nearly 400 people. The owners are accused of closing the doors after the fire broke out to stop looting.