Hillsborough County Fire Rescue units were called to a fire late Saturday at the JCPenney store at Westfield Brandon mall.
The agency said the fire was under control by 12:40 a.m. Sunday.
Several employees who were inside the store when the fire started were able to exit the building and call 911. No injuries were reported.
Crews worked for more than three hours to ventilate heavy smoke from the two-story, 148,000 square-foot building, Hillsborough County Fire Rescue said.
The entire store sustained severe smoke damage, along with water damage on the first floor and fire damage to one area, officials said.
Investigators determined the fire, which started inside a wall, was accidental and caused by an electrical problem.
The JCPenney will remain closed for now, officials said. The rest of the mall is not affected and will be open.