Police say just after 11.30pm last night two employees locked up after finishing their shift at the Parry Street premises.
About 40 minutes later a member of the public contacted emergency services after noticing flames and smoke coming from the building.
Emergency services arrived and a number of people were evacuated from surrounding buildings.
The fire was eventually extinguished, however the building sustained major structural damage.
The bar opened in 2014 and is owned by Silverchair bassist Chris Joannau.