Hundreds of Colorado homes lost and tens of thousands of residents to evacuate amid fast-growing wildfires

Hundreds of US homes have been lost after two wildfires started and grew quickly Thursday as high winds whipped through the Front Range in Colorado.

The fires have forced tens of thousands of residents from their homes, the Boulder County sheriff said.

Sheriff Joe Pelle estimated 580 homes or other structures in and around Superior may have been lost. A shopping centre and a hotel in Superior also were engulfed by the flames.

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Homes burn as wildfires rip through a development near Rock Creek Village, near Broomfield, Colorado. Homes surrounding the Flatiron Crossing mall were being evacuated as wildfires raced through the grasslands as high winds raked the intermountain West. (AP Photo/David Zalubowski)(AP)

"Historic" 129-160 kilometre per hour winds, with gusts as high as 185 kph, fed the wildfires that injured at least six people, prompted a hospital to send patients elsewhere and forced the evacuation of Superior and Louisville near Boulder.

The Marshall Fire had burned at least 1,600 acres and had spread east across Superior and Louisville, the sheriff said.

The other fire is known as the Middle Fork Fire, but there were no details about its size.

A horse runs through Grasso Park as smoke from nearby fires obscures visibility in Superior, Colorado. (Helen H. Richardson/The Denver Post via AP)(AP)

Smoke makes visibility difficult in Louisville, Colorado on December 30.(KMGH)

There currently are no reports of casualties or missing people, Mr Pelle said.

"I'd like to emphasise that due to the magnitude of this fire, the intensity of this fire and its presence in such a heavily populated area, we would not be surprised if there are injuries or fatalities."

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Governor Jared Polis, who declared a state of emergency for the area, said the flames were travelling the length of a football field in just seconds.

"Very little time to get out, very little time to even get the most important parts of your life and, yes, it'll be a difficult process for Colorado families who are directly affected to rebuild their lives," he said.

An estimated 580 homes, a hotel and a shopping centre have burned and tens of thousands of people were evacuated in wind-fuelled wildfires outside Denver, officials said Thursday evening. (Hyoung Chang/The Denver Post via AP)(AP)

Louisville and Superior are about six kilometres apart, not far from Boulder.

At least six people are being treated for injuries related to one of the fires, a spokesperson for UCHealth told CNN.

Kelli Christensen said no more information was available for the patients, who are at UCHealth Broomfield Hospital.

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Another hospital, Avista Adventist Hospital, was prompted to evacuate its patients and employees. The facility has 114 beds, according to its website.

"If you're in the area, please act quickly," the Boulder County Office of Emergency Management tweeted to Louisville residents.

Video from CNN affiliate KUSA showed several homes in Louisville on fire.

The US Census Bureau says Louisville has about 21,000 residents and Superior has 13,000.

"We are in the midst of a truly historic windstorm across the front range, foothills and urban corridor," said the National Weather Service office in Boulder.

Widespread wind gusts of 129-160 kph winds have been observed, the weather service said, and "a handful of sites in Rocky Flats have seen several hours worth of gusts 160-185 kph."

Combined with relative humidity below 20 per cent and ongoing drought conditions, the extreme winds are fuelling rapid fire spread.

County residents have been asked to evacuate if they see flames from one of multiple wildland fires.

The fires are being fuelled by hurricane force winds tearing through Colorado.( KCNC)

"Boulder OEM is getting many calls about residents seeing fire. IF YOU SEE FIRE, EVACUATE. Go east, go north, but leave immediately," the office tweeted.

The hurricane-force wind gusts being reported are being attributed to "exceptional mountain wave amplification," which is a major increase in wind speed as air flows over and down the mountains into the lower elevations that can occur under very specific atmospheric conditions.

High-wind warnings are in effect for portions of Colorado and Wyoming through this evening. Sustained winds of 40 to 64 kph are forecast with gusts exceeding 129 kph.

The "strongest winds below 6000 feet (1829 metres) are expected to be near the base of the foothills from Boulder north to Fort Collins to the Wyoming border," the weather service said.

In addition to quickly spreading fires, these strong winds likely will blow down trees and power lines, which could lead to widespread power outages and difficult travel.

There will likely be a "rapid retreat of the strongest winds back into the foothills" by Thursday evening, the NWS office said.

By morning, the region will experience "weather whiplash," going "from fire to snow," according to the weather service. An advancing cold front will push into the area and bring snow showers to foothills and front range by sunrise.

A winter storm warning is in effect for the region beginning at 5 a.m. MT Friday and calls for 13-25 centimetres of snow by Saturday. The combination of heavy snow and winds associated with the front and terrain will create treacherous travel conditions at time.