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PITMAN, N.J. (CBS) — Crews are at the scene of a four-alarm fire at three-story duplex Sunday afternoon.

Reports came in at approximately 12:30 p.m. about a fire at 57 North Oak Avenue.

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According to fire officials, three firefighters were injured when a staircase into the basement of the building collapsed. The seriousness of their injuries is unknown.

Another two firefighters were being treated by medics, but the reason for their treatment has not been confirmed.

One firefighter was reportedly transported to the hospital by emergency medical services.

Multiple companies were called to help put out the fire including Glassboro, East Greenwich, Mullica Hill, and Clayton fire crews.

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An eyewitness reports that heavy smoke can be seen billowing from the third floor of the building.

The fire is still in progress and not under control as of 1:38 p.m.

Investigators do not know what caused the fire.