Budapest police spokeswoman Katalin Fanni Horvath says thousands of people were caught up in the stampede and the victims may have been trampled by the rushing crowd.
Police have opened an investigation into the organizers and, along with medical investigators, are working to determine the cause of the deaths. Police have denied reports that the victims were stabbed.
The incident occurred late Saturday at the West-Balkan nightclub in downtown Budapest, housed inside a communist-era shopping mall and office complex. Witnesses told Hungarian media on Sunday that the three-floor disco was overcrowded.