Myer Launceston suffered extensive water damage after a fire in a changing room.
After being alerted by Myer's fire alarm, Launceston firefighters arrived at the scene on Saturday afternoon to find the sprinkler system had activated.
Firefighters went to the third floor to find a small blaze that had been extinguished by the building's sprinkler system.
After turning the sprinkler system off, firefighters and Myer staff worked to prevent further water damage to stock across three floors.
The fire is still under investigation, with the matter being handed over to Tasmania Police.