MIAMI -- A demolition crew's job just got easier. A fire at an empty warehouse left the building in the 1800 block of Northwest First Avenue without a roof and firefighters battling extreme temperatures compounded by an already hot day.

Sky 10 was in the air as flames were seen shooting through the roof of the warehouse near downtown Miami on Thursday and thick, black smoke lingered into the sky.

It started about 8:45 a.m. when demolition crews were working inside the warehouse. They were trying to cut away metal shelves from inside when sparks from a torch lit the insulation, Local 10 reported.

Firefighters attempted to cut ventilation holes in the roof, but they were pulled back after the blaze began to quickly spread throughout the building.

"We had a back draft, which basically is a large explosion that came out of the doors where they entered initially," Miami fire-rescue spokesman Ignatius Carroll said. "The fire did do significant damage to the roof, which did cause it to collapse."

A block-and-a-half radius surrounding the building was evacuated, including a nearby elementary school, because of flying debris brought on by intermittent explosions. Traffic was also being diverted from Northwest First Avenue to North Miami Avenue between 15th and 20th streets while firefighters doused the flames from the roof.

"Every so often you'll hear an explosion and see concrete just flying," witness Burke Eastlick said.

Around 1:30 p.m., fire officials said the blaze was under control.

No injuries were reported, but at least one firefighter was being treated for heat exhaustion, Carroll said.

The building is located at 1801 N.W. First Ave.