It happened at 11:30 p.m. Sunday at The Landings of Carneys Point Apartments in the 100 block of Merion Avenue in Carneys Point.
Investigators say the fire broke out in a second floor unit. Flames quickly pushed through the roof.
At least four apartments sustained heavy damage by the time firefighters declared the fire under control at 1:30 a.m. Monday.
All 12 units in the building sustained damage of some kind.
The Red Cross was assisting eight families.
Fire investigators are working to determine the cause.