WEST CHESTER, Pa. (AP) — Authorities in Pennsylvania say a dozen firefighters were overcome by carbon monoxide fumes while battling a building fire.

Officials say firefighters responded to reports of a blaze in West Chester, about 30 miles west of Philadelphia, around 3:30 p.m. Wednesday.

The firefighters were somehow overcome by carbon monoxide, sending one into cardiac arrest.

Chester County officials say several firefighters were hospitalized and others were evaluated at the scene.

It was not immediately clear what caused the fire.