BOULDER, Colo. — A wind-swept wildfire that tore through suburban neighborhoods between Denver and Boulder on Thursday, forcing the evacuation of thousands of people, may have destroyed between 500 and 1,000 homes, the authorities said Friday morning, making it the most destructive blaze in state history.
The fire, as intense as it was sudden, sent tens of thousands of residents of Boulder County scrambling to leave department stores and houses on Thursday as fire trucks swarmed the area. Though wildfires are seen as less of a threat in suburban areas, especially in December, a period of intense drought had created the conditions for the flames to spread, destroying houses, a shopping complex and a hotel.
“It felt like the apocalypse,” said Ruthie Werner, a resident of Louisville, Colo., who had gone to shop at a Target store but arrived to find the parking lot ablaze.
Gov. Jared Polis said at a news briefing that President Biden had approved an expedited major disaster declaration, which allows those who lost their homes or small business to get assistance before the preliminary damage assessment is done. He said schools and major hospitals in the area were spared.
As Mr. Polis toured the damage by helicopter on Friday, video published by a local television station showed how the flames had struck seemingly at random. One house on a cul-de-sac would be destroyed, while the others looked to be intact. In one neighborhood, a line of about 10 still-smoldering rubble piles was next to other houses that had appeared to escape severe damage.
Despite the destruction, no deaths had been recorded, a figure that Mr. Polis said at the news conference would be a “New Year’s miracle” if it held.
“It wasn’t a wildfire in the forest, it was a suburban and urban fire,” said Mr. Polis, a Democrat who lives in Boulder County. “The Costco we all shop at, the Target we buy our kids’ clothes at — all damaged.”
The fire, which began late Thursday morning, burned in a “mosaic” fashion, encouraged by 105 mile-an-hour winds. It torched about 6,000 acres, said Sheriff Joe Pelle of Boulder County, who added that damage assessments were still being done on Friday. The authorities suspect the fire was caused by a downed power line, but that has not been confirmed, he said.
Much of the fire has been contained, with only a few parts of Boulder County still smoldering, he said. Heavy snowfall was in the forecast for Friday, which would help tamp down the fire but could also lead to freezing pipes, officials said.
Louisville and Superior, both about nine miles east of Boulder, suffered the most “catastrophic” losses, he said. Residents of those cities were ordered to evacuate on Thursday, along with residents of nearby Broomfield and Westminster.
While there was no immediate official count of how many people were ultimately displaced, an estimated 200 people are currently staying at emergency shelters in the county, Mr. Polis said.
Evacuees fled the fire zones under plumes of smoke that clouded the sky for miles on Thursday, not knowing if their houses would make it through the night. Roads and highways in the Denver metro area were jammed with thousands of residents trying to flee.
“It took us almost an hour to get out of our neighborhood — it was complete gridlock,” said John Stein, who was walking his dog in Superior when he saw smoke in the area and heard sirens.
Thomas Maxwell, 25, said he did not know on Thursday if his parents’ house in Louisville was still standing. Mr. Maxwell, who lives in California, had been dog-sitting for them while they vacationed in Spain. He woke them with a midnight call to say that he had evacuated to a hotel with their two dogs.
“It was crazy how fast it happened,” Maxwell said. “I read about wildfires in California all the time. Now I’m experiencing it. It’s so different.”
Wildfires in the American West have been worsening — growing larger, spreading faster and reaching into mountainous elevations that were once too wet and cool to have supported fierce fires. What was once a seasonal phenomenon has become a year-round menace, with fires burning later into the fall and into the winter.
Recent research has suggested that heat and dryness associated with global warming are major reasons for the increase in bigger and stronger fires, as rainfall patterns have been disrupted, snow melts earlier and meadows and forests are scorched into kindling.
Colorado had the three largest wildfires in its history in the summer of 2020, each one burning more than 200,000 acres, Mr. Polis said. But those fires burned federally owned forests and land, he said, while the fires on Thursday destroyed suburban developments and shopping plazas.
“As a millennial, I’m just looking outside and I’m seeing climate change,” said Angelica Kalika, 36, of Broomfield. “I’m seeing my future. I grew up in Colorado, and this is a place where I’ve had snowy Christmases and a nice 60-degree summer. But, for me, this is a moment of deep reckoning of climate change when there is a wildfire outside my door.”