CHICAGO — More than 200 firefighters responded to a massive blaze that engulfed a West Ridge strip mall Friday evening.

A fourth alarm was raised at 5:30 p.m. as crews battled the fire at 3106 W. Peterson Ave. The fire was struck out just before 6 p.m., according to fire department spokesman Larry Langford.

Crews were dispatched to the strip mall about 4 p.m. Officials believe the fire originated in the American Mattress store in the strip mall, Langford said. Roofers were reportedly working with torches at the store just before the fire began, he said.

"We don't know if that's the cause, but it's being looked at," Langford said.

As of 7 p.m., the workers who had been on the roof could not be found to be interviewed, authorities said.

Three stores - American Mattress, Mid-America Furniture and Four Eyes - were destroyed by the blaze. Deputy Fire Commissioner Michael Callahan said there was a "catastrophic collapse of the roof and walls" in the affected stores, but said nobody was hurt in the fire.

"To the best of my knowledge, when the companies arrived, the stores were empty," Callahan said. "They self-evacuated."

Callahan said crews were initially called to the For Eyes Optical store, and it was quickly determined the fire was too involved and needed to be fought from outside the building.

Firefighters performed a "trench cut" in the building's roof, and a fire wall on the west side of the American Mattress store prevented the fire from spreading to the rest of the strip mall, Langford said.

Crowds gathered for hours to watch as firefighters battled the blaze. Jason Gialunni, 27, who lives nearby, said he heard three large "booms," which he thought may have been generators.

"I'm not gonna lie. It was pretty scary," he said. "When you hear a 'boom,' you can distinguish if it's far, but this 'boom' had a lot of bass in it.

"You could feel the power and the velocity of it," Gialunni said. "It was wild."

Stretches of Peterson and Lincoln avenues were shut down due to the fire, and Callahan said firefighters would most likely remain on the scene throughout the night.

The affected stores would most likely have to be torn down, Callahan said.