DENVER (CBS4)– Investigators say illegal hash oil extraction is the cause of an explosion that left people injured.

The explosion happened on Tuesday afternoon in a garage near 48th and Hooker, north of Interstate 70, in Denver.

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(credit: Denver Fire Dept.)

Two people were rushed to the hospital with burns. It is unclear the extent of the injuries.

Greg Pixley with the Denver Fire Department says the illegal butane hash oil extraction was underway in the garage behind the home in the alley. The explosion blew out two exterior walls on the garage.

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The structure is considered unstable.