ANAHEIM, Calif. (AP) — Authorities say two firefighters were injured in an explosion during a fire at an illegal marijuana extract operation hidden at a commercial building in Southern California.

Fire officials say the blast occurred while fire crews were battling the blaze Sunday at the single-story structure in Anaheim.

One firefighter suffered minor burns to his face. The other hurt his back when he was knocked back by the explosion. Both are expected to recover.

One arrest was made.

Authorities suspect a concentrated extract of marijuana known as honey oil was being produced at the building.