Firefighters found heavy fire when they arrived at the Water World boat dealership on South Miami Boulevard on Wednesday morning, they reported.
Multiple units were dispatched about 6:30 a.m. to the building at 135 S. Miami Blvd.
The first units to arrive said they had to break through a gate to reach the rear of the building where the fire was located.
Fire hoses stretched across the road from a nearby hydrant forced officials to shut down traffic.
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Deputy Chief Iannuzzi said the building was heavily damaged, and firefighters were still working to put out the blaze at 8 a.m.