Witnesses said the blaze broke out when a performer staging a nightly "fire show" inadvertently set his clothes alight, official said.
City prosecutors have begun an inquiry into safety at the 911 club.
It is the latest in a series of disasters that has highlighted Russia's poor enforcement of safety regulations.Officials said first accounts suggested that the blaze broke out when a performer accidentally set his clothing on fire. Flames spread to a large container of spirits and then the nightclub's stage caught fire.