Thousands of people have evacuated towns outside Boulder, Colorado, after hurricane-force gusts ripped down power lines, sparking several grass fires.
The wind gusts reached as high as 110mph 177kph, according to the National Weather Service.
Officials ordered residents in the towns of Superior and Louisville, which have a combined population of 33,000, to flee.
“If you are in Louisville, this is a life threatening situation. Leave Now!,” the National Weather Service said on Twitter.
Radar images from the weather service showed a plume of smoke that stretched for more than 70 miles.
Hundreds of homes have been destroyed, and more than 47,000 homes and businesses across the state are without power.
The swiftly spreading prairie grass fire was believed to have been ignited by sparks from power lines and transformers toppled by high winds on Colorado’s drought-parched Front Range, according to Boulder County Sheriff Joe Pelle.
Evacuation orders were first issued for all residents in the town of Superior, Colorado, with a population of about 13,000, and a short time later for the adjacent municipality of Louisville, home to more than 18,000 residents, the Boulder County emergency management office said on Twitter.
Within hours, the blaze had swept an estimated 1,600 acres (647.5 hectares) and destroyed more than 500 homes, Mr Pelle told reporters at a news briefing.
He said an entire subdivision of 370 homes went up in flames west of Superior, and that 210 dwellings were lost in the Old Town area of Superior, along with additional residences in the area. Property losses also included a shopping centre and hotel in Superior, officials said.
Governor Jared Polis said flames were consuming football fields of landscape in a matter of seconds, calling the conflagration “a force of nature”. – Agencies