No one was hurt when firefighters arrived at the Lakewood Condos in Osage Beach about 7:30 p.m. on Saturday night.
When firefighters first arrived at the scene, flames and smoke were showing on the water side of building 400. Heavy fire was burning in the attic. A firewall stopped the flames from spreading to building 500.
It took firefighters about 90 minutes to get the fire under control. Fire investigators still don't know how it started.
Osage Beach Fire Marshal Ed Nicholson said, "The point of origin is in the area of the propane fireplaces on the top floor."
Firefighters left the scene about 11:30 p.m. after they gathered evidence for their investigation.
There were six people in this building during the fire. They evacuated themselves before firefighters arrived at the scene.
Fire codes do not require these older condos to have pull down fire alarms. Tenants depended on smoke detectors and people knocking on doors to get them out safely.
"In a new complex there would be. In this one, it's older. Back in the 80s, it wasn't a requirement then," Nicholson said.
Fire officials are working with insurance adjusters as they continue to investigate the cause of the fire. Early damage estimates are at about $100,000.