Two firefighters suffered minor injuries in an overnight fire at a Naperville duplex, authorities said Saturday.

The blaze was reported by a passerby shortly after midnight at a two-story home on the 2500 block of Eldorado Lane, Naperville firefighters said in a news release.

Firefighters arrived and discovered heavy flames on the second floor at the rear of the home. No one was home in either unit at the time.

Firefighters went at the blaze, the worst of which was in a bedroom, and had it under control by 12:30 a.m.; the fire was extinguished by 2:30 a.m., according to the release.

Naperville police assisted on the scene.

The injured firefighters were examined on the scene for possible muscle strains and released, authorities said.

The cause of the fire was under investigation Saturday. The home where the blaze began was deemed uninhabitable; damage was estimated at $200,000.