Four people were injured Friday in an explosion at a Federal-Mogul bearing plant in Blacksburg, Va., The Roanoke Times reported. Two of the victims were airlifted to Wake Forest University Baptist Medical Center in Winston-Salem, N.C. with critical injuries while two others were taken to a local hospital with minor injuries. The explosion was heard at the Federal-Mogul Corp. plant just after 9:30 am ET. No cause for the blast was identified. Federal-Mogul spokesman Jim Burke confirmed that the victims they were not Federal-Mogul employees, but were working for a local contractor cleaning at the plant. According to The Times, fire trucks and other emergency vehicles remained at the scene and the perimeter of the plant was blocked off. The plant, which specializes in manufacturing bearings, is one of 107 worldwide Federal-Mogul plants.