Firefighters struggled today to beat back a wildfire raging at the edge of Colorado Springs that doubled in size overnight, forcing more than 32,000 people from their homes.
The blaze, fanned by hot winds, has charred a number of homes on the wooded edges of the city.
US President Barack Obama plans to travel to the area tomorrow to view the damage.
But in the chaos of the fire's advance, officials could not say exactly how many homes were lost or how many more people might join the ranks of the displaced.
Colorado Springs Fire Chief Rich Brown called the firestorm threatening his city - in a metropolitan area of more than 650,000 people - "a monster" and said at this point flames were "not even remotely close to being contained."
Colorado wildfires have killed four people this year, but no serious injuries from the Waldo Fire were reported today.
"This is the worst fire season in the history of Colorado," Governor John Hickenlooper told a news conference yesterday, after he flew into Colorado Springs to tour the fire zone.
Over half of the federal government's firefighting resources are deployed in Colorado, the White House said.
At a service station in Colorado Springs, Andrew Heintzelman, 34, said he had been on the roof of his home in the nearby community of Mountain Shadows yesterday trying to keep the flames at bay but had since been forced to flee.
"I was spraying the hose on the shingles and the cops came through the neighbourhood and told me to get out now," said Mr Heintzelman, 34, who lives with his mother.
Thunderstorms in the area were expected to hurt firefighting efforts by causing erratic winds, which could shift from one direction to the next, fire officials said.
"All that kind of squirrelly behaviour makes it really unsafe for anyone to be in or around the fire," fire information officer Anne Rys-Sikora said.