"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 Tuesday.

"I don't think anyone expected that this would happen."

The growing blaze around 100 kilometres south of the state capital Denver compounds the struggle for fire fighters battling wildfires across the American West, where temperatures have soared in recent days.

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 2 480 hectares and is just five percent contained.

Officials declined to estimate the number of homes destroyed, but feared the figure would be high.

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 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 100 kilometres an hour have fuelled blazes across the American West.

Firefighters in Colorado were battling two other fires along the front range of the Rocky Mountains, including the High Park fire, near Fort Collins, about 100 kilometres north-west of Denver.

That fire, which started on June 9, has now consumed 34 800 hectares, making it the second largest fire in Colorado history. The blaze, which was ignited by lightning, is now 65% contained.

Fire fighters are also working to keep the Flagstaff Fire – estimated at just over 88 hectares – away from the city of Boulder, home to Colorado University.