The fire started just before 6 p.m. on 9201 John F. Kennedy Boulevard West.
Flames shot through the roof of the building, and smoke could be seen from Manhattan.
Investigators believe the blaze began as an electrical fire on the 5th floor, and then spread to the cockloft. The fire then refused to die, spreading from one part of the complex to the other, engulfing the 120-unit structure, and leaving hundreds of residents without a place to live.
One firefighter suffered broken ribs after falling down some stairs. His injuries are not life-threatening.
Residents were evacuated from the building, and hundreds were left displaced.
The Red Cross and Mayor of North Bergen announced that a shelter was setup at a local high school.
Some of the displaced residents had a reason to smile Sunday as they reunited with their pets. North Bergen firefighters brought out cats, dogs, birds and even a turtle. Then they went down the list, and put pet owners and their pets together.
However, the bad news is 9201 Kennedy Boulevard is in bad shape. A North Bergen Township official says repairs could take months, and that the building may need to come down.
The neighboring apartment building that was evacuated Saturday night as a precaution was not damaged.