The fire was located in the 5700 block of 128th Street in Crestwood, fire department officials said.
Fire crews responded to the scene around 5:30 p.m. and were able to extinguish the fire quickly, officials said.
Four adults were taken to hospitals. One was in serious condition and three were in good condition.
The 12-unit apartment building is now uninhabitable, officials said. The Red Cross is helping displaced residents.
No further information was immediately available.