Firefighters responded to the three-story apartment building in the unit block of Huron Avenue in Norwood just before 2:30 a.m.
Police officers entered the burning building and helped rescue several residents who were on the top two floors.
Crews got the fire under control within an hour.
Firefighters say those being treated at the hospital did not appear to have life-threatening injuries.
The Red Cross is helping more than 20 residents who are displaced.
The cause of the fire is under investigation.
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