Neighbors said they heard a loud explosion and people screaming for help before fire engulfed the building in the 1200-block of Harding Avenue.
Flames could be seen billowing from the roof of the three-story apartment building.
The fire chief said five people were taken to the hospital. Their conditions were not immediately known.
Neighbors rushed to help each other get to safety.
"We were helping a lady get off the building and we saw another gentleman on top of the building, he was badly burned," neighbor Mike Motschman said.
One woman said neighbors put a trash can under her window and she jumped from her window.
She was physically OK when she shared that, but was emotional talking about what happened.