Fire investigators are trying to determine the cause of an apartment building fire that caused extensive damage and injured four people.

Firefighters were called to the Salem Village Apartments in Newark around 4 a.m. Friday. When they arrived they found quick moving flames and heavy smoke pouring from the apartment building. A second alarm was sounded bringing extra fire companies to the scene to assist. 

It's not clear what caused the fire, but State Fire Marshal Deputies are on the scene this morning trying to determine what sparked the blaze. 

Three residents and one firefighter were injured. There's no word on the extent of those injuries. Damage to the building is considered extensive.