Tens of thousands of Americans are waiting to find out if their homes have been destroyed by a fire.
The fire, one of several blazing across the front range of the Rocky Mountains, has torched more than 7000 hectares, and has reportedly destroyed some 300 homes, though no official figure has been given.
At a Red Cross evacuation centre, some of the 36,000 displaced people waited on Wednesday night for word of whether their homes and belongings had been destroyed.
Fire Incident Commander Rich Harvey told reporters there was concern the wind was pushing the flames toward Colorado Springs, which was already enveloped by a heavy plume of smoke.
More than 8400 people, 578 fire trucks and 79 helicopters have been deployed to tackle wildfires around the United States, the White House said.
The Denver Post published an aerial photograph on Wednesday that it said showed some 300 houses had been destroyed in the Mountain Shadows neighbourhood within the limits of Colorado Springs, the state's second largest city.
Officials have declined to give a precise count, saying they have not been able to visit the charred areas because of the intense heat.
Summer wildfires are common in the mountains of arid Colorado but they rarely burst into residential areas, as the Waldo Canyon Fire did earlier this week.
Firefighters are battling several other fires in the state and in neighbouring Utah.
US President Barack Obama plans to visit the state on Friday and spoke to Colorado Governor John Hickenlooper and Colorado Springs Mayor Steve Bach on Wednesday.
It was not immediately clear what sparked the Waldo Canyon Fire but Hickenlooper suggested it was not lightning.
"There's suspicion out there that we've got some idiot," he told CNN. "We're working as hard as we can to approach and get the real facts and not jump to conclusions."