After 11 hours, firefighters controlled the blaze that raged through the SuperCheap department store in the southern resort of Phuket since 9.30pm last night, sending flames hundreds of metres into the air.
No casualties were immediately reported, and the cause of the incident was not known.
Emergency workers controlled the perimetre of the 35 rai (14 acres) department store but flames were still burning inside warehouses which could not be reached by the firefighters.
Fire engines hosed water from outside the building complex.
A Royal Thai Navy helicopter to spray foam to contain the fire inside the building, as the Phuket governor vowed to completely extinguish the fire by midday.
The department store employs as many as 700-1,000 staff and the authorities are checking to see whether any died or were injured in the fire.