The blaze in south-central Custer County was quickly spread by 50 mph winds, The Denver Post reported.
The high winds prevented crews from fighting the fire from the air.
Officials said the wildfire was ignited by a house fire in a subdivision south of Wetmore and that it had burned into "broken terrain" of relatively uninhabited areas of Custer and Pueblo counties.
More than 300 homes have been evacuated, said Steve Segin of the Rocky Mountain Area Coordination Center.
A separate wildfire in Estes Park has consumed 979 acres and was only partially contained, the National Park Service reported.
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