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ALLENTOWN, Pa. (CBS) – Crews are still dousing hot spots after a four-alarm fire broke out at a warehouse being converted into apartments in Allentown on Sunday night. At least one firefighters has been injured in the blaze.

The firefighter was taken to a nearby hospital after burning his hand and was treated and released. Firefighters arrived to the area of Warren Street and North Franklin Street just before 6:30 p.m. Sunday.

Flames were shooting out of windows and engulfed the top of the unoccupied warehouse.

“I saw it last night. I was at my window and I was actually about to lay down when I saw all the smoke go by,” said neighbor Khadijah Vega. “When I saw it, I was like, ‘Oh, snap, the building is on fire.'”

Allentown police say the old factory was being converted into apartments and that the lumber stored inside the factory for the renovation helped fuel the massive fire.

Authorities are not yet sure what caused the fire, but say the 100-year-old building is so badly damaged it’s not safe for anyone to enter, even firefighters.

Officials say the building was so badly damaged that demolition will begin tomorrow.

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Other people have been told to shelter in place in case it comes down.