A natural gas explosion at an Oak Park apartment building Wednesday caused a fire, knocking down portions of a wall and injuring one person, officials said.

Fire officials responded about 5:30 p.m. to a fire with collapsed sections of a wall at a residential building in the 200 block of South Maple Avenue, Oak Park spokesperson Dan Yopchick said.

A man was taken to Loyola University Medical Center, where his condition was unknown, officials said. His age was also not known.

About 12 other residents of the building were displaced, as all six apartment units were considered uninhabitable after the fire was extinguished, Yopchick said.

A preliminary investigation indicated that the fire began from a natural gas explosion inside the building, officials said.

An investigation is ongoing.