Firefighters respond to a fire at a portable classroom at Joppatowne High School. (The Aegis, Bryna Zumer / May 30, 2013)

A fire caused about $5,000 in damage to a portable classroom outside Joppatowne High School on Wednesday, the Joppa-Magnolia Volunteer Fire Company reported.

Firefighters responded to the call at about 10:09 a.m. Smoke was reported showing from the one-story classroom.

"A small fire was quickly extinguished inside the walls and ceiling of the classroom," the Joppa-Magnolia company reported in an e-mail. "The source of the fire was found to be a malfunctioning air conditioning unit that was attached to the classroom."

The state Fire Marshal's Office was notified, but did not respond to the scene.

No one was injured.

Nearly 40 firefighters from Joppa-Magnolia, Kingsville, White Marsh, Bel Air and Aberdeen volunteer fire companies responded, as did Aberdeen Proving Ground Fire Department.