A house explosion in southwestern Indiana that injured three people has been traced to a heater that began leaking natural gas during maintenance work, authorities said.

Four people were inside the two-story home when it was heavily damaged by Tuesday's explosion in the city of Princeton, leaving two people hospitalized with burns while a third person complained of back pain, the Indiana Department of Homeland Security and State Fire Marshal said.

Princeton Fire Territory Chief Nick Medler said two maintenance personnel were working on a wall-mounted gas heater on the home's second floor when it malfunctioned, causing the gas leak.

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"In messing with that furnace, we’ve come to this incident," Medler told WFIE-TV on Wednesday.

Indiana News

An Indiana house explosion injured three people after a gas leak caused by maintenance workers ignited. (Fox News)

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The Department of Homeland Security and State Fire Marshal said the leaking gas was accidentally ignited, causing the explosion in the city about 25 miles north of Evansville.

Medler said Thursday that investigators could not determine what ignited the gas. He said the home’s occupants were "very fortunate" because they suffered injuries not believed to be life-threatening.

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Medler said the home's four occupants were able to walk out of the damaged residence on their own after fire crews arrived at the scene Tuesday.