A wildfire swept through a residential area near the city of Colorado Springs, destroying homes and prompting orders to move some 32 000 people to safety, authorities said.
"This is a firestorm of epic proportions," Colorado Springs Fire Chief Rich Brown told a news conference late on Tuesday.
The fire, which began in Waldo Canyon on Saturday, exploded into the community of Mountain Shadows on Tuesday afternoon and set the ablaze the mountains that rim the city 100km south of the state capital, Denver.
Among the areas threatened was the US Air Force Academy, which evacuated two housing areas, a day before the scheduled arrival of 1000 new cadets, the academy said.
Soaring temperatures compounded the agony for firefighters trying to contain the 6000 acre (2400 hectare) blaze, one of many raging across the American west.
The Waldo Canyon fire has spread quickly since it began on Saturday, and turbulent winds on Tuesday afternoon prompted authorities to seek evacuations of up to 32 000 residents.
There were no reports of anyone killed or wounded in the fire, which has consumed 6200 acres (2480 hectares) and is just five percent contained.
Officials declined to estimate the number of homes destroyed, but feared the figure would be high.
"Up until this afternoon this was a wildfire, and then it hit the northwest subdivisions," Mayor Steve Bach of Colorado Springs, the state's second largest city, told KDVR-TV late on Tuesday.
"I don't think anyone expected that this would happen."
Owners of the Flying W Ranch, a working cattle ranch known nationally for its western-style restaurant, said on their website that it had been "burned to the ground."
Colorado Governor John Hickenlooper raced to the scene on Tuesday night to tour the area by air.
"We saw a pretty grim scene. The devastation is pretty intense," the governor told KCNC-TV, adding that the only bright spot was that there were no reports of loss of life.
Record high temperatures, extremely low humidity and wind gusts of up to 100km/h have fuelled blazes across the American West.
The state of Utah meanwhile also is combatting a major fire, which through more than 6000 acres of grassland in an area about 45 minutes south of Salt Lake City.
Tinder-like conditions were created by this year's unusually mild and dry winter, officials said.
Firefighters in Colorado are battling two other fires along the front range of the Rocky Mountains, including the High Park fire, near Fort Collins, about 100km northwest of Denver.
That fire, which started on 9 June, has now consumed 87 000 acres (34 800 hectares), making it the second largest fire in Colorado history. The blaze, which was ignited by lightning, is now 65 percent contained.
Firefighters are also working to keep the Flagstaff Fire — estimated at just over 200 acres (88 hectares) — away from the city of Boulder, home to Colorado University.