A building caught in fire on Saturday afternoon on Tremont Street in Boston.
The fire was reported at 801 Tremont St. in the South End. An off-duty firefighter at the scene called and alerted the fire station, and proceeded to alert other residents by knocking on their doors to evacuate the building, according to the Boston Fire Department.
Officials said the fire was on the first floor of the four-story building and caused heavy smoke conditions throughout, making the evacuation of elderly residents difficult for firefighters.
There were no residents at home in the unit where the fire started, and all other residents of the building were safely evacuated.
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One firefighter was taken to an area hospital for minor injuries, said authorities.
Boston EMS said two apartments housing five residents were affected by the fire, with damages estimated at $150,000.