CHICAGO — A Chicago firefighter is OK after falling through the second-floor of a house into the basement while battling a fire in the city’s North Lawndale neighborhood.

A second firefighter is hospitalized in good condition with a knee injury.

The blaze broke out in the back of a home on the 1200 block of South Komensky Avenue around 4 a.m. Thursday.

According to fire officials, crews believed there were residents inside the structure and began an immediate attack upon arrival.

As fire crews entered the home, a portion of the second-floor collapsed and a firefighter fell through into the basement — but landed on a mattress. He was uninjured.

A Mayday was called due to protocol.

A firefighter injured his knee while exiting the house. He was transported to an area hospital in good condition.

All residents safety escaped the property.

The cause of the fire is under investigation.