City firefighters said they found fire in the walls and floors of apartments on all three floors of the Main Street building.
It took time to complete the job because of "an electrical issue throughout the building, which is what led to the fire being in several apartments," the department said.
PSE&G responded to cut power.
No injuries were reported.
Joining Hackensack's bravest at the scene were their firefighting colleagues from Englewood, Teaneck, Ridgefield Park and Bogota, as well as city police and local EMS.
Tenafly, Maywood, Little Ferry and River Edge were among those departments providing backup.
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