The flames broke out shortly after 12:30 Friday afternoon on the 8000 block of Ditman Street.
A second alarm was struck less than 15 minutes later.
The flames tore through several units of the six unit building.
Three injuries were reported. Two people suffered smoke inhalation.
A woman in her 70s, who neighbors say used an oxygen tank, suffered severe burns. She is listed in critical condition.
"One critical female was transported to Aria-Torresdale, and one adult male and one adult female were transported to Nazereth Hospital," said Battalion Chief Michael Richey, Philadelphia Fire Department.
The flames were brought under control shortly before 1:20 p.m.
The Red Cross is assisting those residents who have been displaced.
No word yet on a cause.