GWINNETT COUNTY, Ga. -- Fire officials said a dog was the lone victim of a Gwinnett apartment fire being blamed on "careless smoking."

The fire happened at the KRC Reserve Apartments off of Jimmy Carter Blvd. just north of Tucker around 10 a.m. Saturday. Crews arrived to find the fire already burning heavily in the attic of a split-level apartment building.

Fire fighters immediately went on the attack with rescue the priority as they hit the building with water and began their search of the building. The fire caused heavy damage to the unit where the fire began and minor damage to the apartment below.

Fire crews worked quickly to prevent the spread of the fire, which resulted in only one report of injury by an occupant who was checked out by paramedics on the scene.

Fire investigators believe it began as a result of careless smoking and a "medical oxygen hazard."

Two families are now seeking help from the American Red Cross as a result.