The flames broke out before 11 a.m. at a vacant 2-1/2 story residence in the 800 block of South 14th Street.
The fire quickly extended to two neighboring structures, both occupied three-story wood frame residences.
Newark Public Safety Director Brian O'Hara said the firefighter sustained a minor injury to his neck.
He was evaluated at the scene by EMS and remained on duty.
No other injuries were reported, but seven families, including 15 adults and eight children were relocated from the neighboring buildings.
The fire was considered under control at 12:32 p.m.
The cause and origin of this fire is under investigation by the Department of Public Safety's Arson Unit.
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