State and local authorities are investigating what sparked an overnight explosion that rocked a suburban Chicago apartment complex, seriously injuring two people and showering the area with debris.

Police and firefighters who were called to the scene of Tuesday’s explosion and subsequent fire in Oak Forest found two people with serious injuries, officials said. Both were transported to a nearby hospital for treatment.

Television footage from the scene on Wednesday morning showed broken glass and other debris from an apartment building scattered across the ground outside as investigators and officers inspected the area. It is believed that the explosion occurred in one of the apartments.

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The Oak Forest Police Department said Wednesday in a Facebook post that an initial investigation revealed that there was “an explosion of unknown origins within the unit.”

Illinois authorities are investigating the cause of an apartment building explosion near Chicago.

Oak Forest police are investigating the blast along with the State Fire Marshall, the Illinois Department of Natural Resources’ Explosives Unit and the Bureau of Alcohol, Tobacco, Firearms and Explosives.

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Neighbor Reggie Odell said the explosion around 7 p.m. shook all his windows and doors in the Chicago south suburb.

“I was laying down watching TV in my bedroom when all of sudden I heard an explosion,” he told WMAQ-TV.

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Odell said that when he exited his apartment and walked towards the parking lot, he saw that the windows and doors of a neighboring building had been “blown out.”