Sheriff Joe Belle estimates the Superior and 580 homes or other structures around it may have been lost.
A shopping center and hotel in Superior were also gutted by the fire.
“Historic” winds of 80-100 mph, 115 mph, fed wildfires that injured at least six people, prompted the hospital to relocate patients and forced the evacuation of Superior and Louisville near Boulder.
The Marshall fire burned at least 1,600 acres and spread eastward across Superior and Louisville, the sheriff said. The other fire is called the Middle Fork Fire, but there are no details about its size.
Belle said there was currently no information on casualties or missing persons.
“I would like to emphasize that due to the magnitude of this fire, the intensity of this fire and its presence in a highly populated area, we would not be surprised if injuries or casualties occur.”
Governor Jared Police declared a state of emergency in the area, saying the flames traveled the length of a football field in seconds.
“With so little time to get out, so little time to get to the most important parts of your life, yes, rebuilding the lives of directly affected Colorado families can be a daunting task,” he said.
Louisville and Superior are about 4 miles, not far from Boulder.
At least six people are being treated for injuries related to a fire, a spokesman for UCHealth told CNN. Kelly Christensen said no further information was available for patients at UCHealth Broomfield Hospital.
Another hospital, Avista Adventist Hospital, was forced to evacuate its patients and staff. According to its website, the facility has 114 beds.
The U.S. Census Bureau says there are about 21,000 residents in Louisville and 13,000 in Superior.
“We’re really in the middle of a historic wind storm on the front porch, the foothills and the urban sidewalk,” the National Weather Service office in Boulder said.
Widespread winds of 80-100 mph have been observed, the meteorological service said, adding that “a few sites in Rocky Flat saw speeds of 100-115 mph worth several hours.”
District residents have been asked to evacuate if they see flames from several wildfires.
The so-called “exceptional mountain wave amplitude” hurricane-force wind velocity causes a large increase in wind speed as the wind blows up and down the mountains to lower areas that may occur under certain atmospheric conditions.
Extreme winds are expected in parts of Colorado and Wyoming until this evening. Winds are forecast at 25 to 40 mph and at 80 mph.
“Strong winds below 6000 feet are expected, from the northern Boulder to Fort Collins near the foothills of the Wyoming border,” the meteorological service said.
As the fire spreads rapidly, these strong winds can knock down trees and power lines, leading to widespread power outages and difficult travel.
The NWS office said there would be a “rapid reversal of strong winds in the foothills” by Thursday evening.
According to the meteorological service, in the morning, the area will experience “weather whiplash” and “go from fire to snow”. The forward-going cold will be pushed into the area, bringing snow to the foothills and the frontier at sunrise.
A winter storm warning is in effect in the region of 5 MT by Friday morning and 5-10 inches of snow by Saturday. The combination of heavy snow and wind associated with the front and the terrain will create treacherous travel conditions in time.
CNN’s Haley Brink and Brandon Miller contributed to the report.
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