CHICAGO (CBS) — About 20 apartments were left uninhabitable Monday night, after a fire broke out in Westmont.

The fire started around 9 p.m. at an apartment building near 60th Street and Cass Avenue. A resident called 911, saying an apartment was filling with smoke.

By the time the first firefighters arrived, the four people living in that apartment had fled to their balcony to escape the heavy smoke and flames. Firefighters used ladders to rescue them.

The fire was contained to a single upper-level unit.

Everyone living in the 20-unit building was evacuated, but due to the quick actions of the firefighters, no one was injured.

“Got in there, knocked the fire and controlled it to the one unit. We had a lot of heavy smoke damage through the rest of the building,” Westmont Fire Chief Dave Weiss said.

About a dozen suburban fire departments were called in to help put out the fire. The American Red Cross was providing assistance to the 20 families affected by the fire.

The cause of the fire was under investigation.