Occupants all got out safely and no injuries were immediately reported.
The three-alarm fire broke out in the Dickinson Manor condominiums in the Fardale section of town shortly after 5 p.m.
Township firefighters moved quickly and in sizable numbers from the front and rear of the building to prevent the blaze from doing more serious damage.
Firefighters from Waldwick, Wyckoff and Allendale were among those who joined their Mahwah colleagues at the scene, along with township police and EMS.
Tallman FAST, Hillburn Engine, Suffern Tower Ladder and Sloatsburg firefighters also provided mutual aid, along with companies from surrounding towns.
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