JACKSON, Wyo. (AP) — Jackson firefighters say a fire alarm alerted them to a hidden blaze burning in a condo complex.

The renters living in the first-floor unit said they were unaware of any problem when firefighters responded to an alarm in the empty, second-story unit on Saturday night.

Battalion Chief Mike Moyer told the Associated Press that firefighters spotted a "glow" as they walked around the building. The source turned out to be a fire that apparently had spread from fireplace into the area under the building's roof.

It took 30 firefighters about five hours to put out the fire. Moyer said the building will need "significant repair" but a lot more of it would have been lost if not for the fire alarm.