Revellers were ushered out of The Backroom shortly after 10pm as the fire service and police made their way to the scene.
An extractor fan on the roof caught fire, causing a smouldering fire and 'smoke everywhere' in the 1920s themed cocktail bar and nightclub.
A bouncer said: "It is still smouldering. Everyone has been evacuated. We had only just opened so there was only a handful in there."
Three fire engines from Leeds and one from Hunslet attended, with traffic on Call Lane blocked for a short time.
Firefighters had to cut a hole in the roof to get to the fire with two hose reels, as well as going in by the back entrance.
Clubbers had been set to enjoy a Mexican Fiesta with £2 tequilas and Latin and Reggaeton music before their night was cut short.
The was dealt with by midnight and the club reopened.