The department store's section that was hit by fires has been under renovation since early this month.
No deaths or injuries were reported except for a hotel maid who fainted after inhaling smoke.
The fire, which broke out at 10am, was reportedly sparked in a main circuit box on the first floor. It took some 40 firetrucks and firefighters up to 20 minutes to get the blaze under control. The hotel was evacuated as a precaution.
Police say the fire might have been started from welding sparks falling onto piles of inflammable materials or a short circuit. The site has been sealed for damage assessment and investigation.