The Illinois State Fire Marshal is currently investigating the cause of a fire that destroyed eight planes at an airport in the city of Monmouth.

The fire broke out Friday morning, in the Monmouth Municipal Airport’s hangar, a spokesperson for the city confirmed to Fox News. Firefighters responded to reports of heavy smoke emanating from the hangar just before 6 a.m., but found the structure “fully involved” upon arrival.

The Illinois State Fire Marshal is currently investigating the cause of the fire. (City of Monmouth)

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A total of 10 privately owned planes were inside the hangar when the fire broke out. Eight were a “total loss,” a spokesperson confirmed. The damaged aircraft included Cessna and Piper models, as well as an airport-owned plane.

The damaged hangar also included the airport’s administration office.

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Firefighters from several nearby fire departments responded to the scene, and were able to contain the blaze within three hours, according to officials.

"Eight of the planes were a total loss," a spokesperson for the city said. (City of Monmouth)

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The Monmouth Municipal Airport, which is open for public use, was established in 1921. It is said to be the oldest continually operated airport in the state of Illinois, according to the city.