ERIE, Colo. - Authorities in Colorado are responding to an explosion at a middle school east of Boulder that reportedly injured some contract workers. School is still on summer break.

Mountain View fire spokeswoman Laura McConnell says multiple injuries have been reported at Erie Middle School, but there are no details on the extent.

The Daily Camera (http://bit.ly/R9j4J6 ) reports that three contractors were injured in the explosion. A school district spokesman told the newspaper the explosion may have been caused by a hot water heater.

Students aren't set to return to class until Aug. 16.

Erie is about 14 miles northeast of Boulder