Nearly 1,000 homes have been destroyed, hundreds more damaged, and three people are missing after a winter wildfire hit a suburban area at the base of the Rocky Mountains in Colorado.
The wind-whipped wildfire blackened entire neighbourhoods in the area between Denver and Boulder.
Boulder County Sheriff Joe Pelle said investigators are still trying to find the cause of the blaze that erupted Thursday.
Pelle said utility officials found no downed power lines around where the fire broke out. He said authorities were pursuing a number of tips and had executed a search warrant at "one particular location."
The news came as an overnight dumping of snow and frigid temperatures compounded the misery of hundreds of Colorado residents who started off the new year trying to salvage what remains of their homes.
At least 15 cm of snow and temperatures in the single digits cast an eerie scene amid the still-smouldering remains of homes. Despite the shocking change in weather, the smell of smoke still permeated empty streets blocked off by National Guard troops in Humvees.
For the thousands of residents whose homes survived the conflagration, Red Cross shelter volunteers distributed electric space heaters as utility crews struggled to restore natural gas and electricity.
At least seven people were injured in the wildfire that erupted in and around Louisville and Superior, neighbouring towns about 32 kilometres northwest of Denver with a combined population of 34,000.
Families forced to flee the flames with little warning began returning to their neighbourhoods on Friday to find a patchwork of devastation. On some blocks, homes reduced to smoking ruins stood next to ones practically unscathed by the fires.
Cathy Glaab found that her home in Superior had been turned into a pile of charred and twisted debris. It was one of seven houses in a row that were destroyed.
"The mailbox is standing," Glaab said, trying to crack a smile through tears. She added sadly, "So many memories."
Despite the devastation, she said they intend to rebuild the house she and her husband have had since 1998.
As the flames swept over drought-stricken neighbourhoods with alarming speed, propelled by guests up to 169 km/h tens of thousands were ordered to flee.
With some roads still closed, people walked back to their homes to get clothes or medicine, turn the water off to prevent the pipes from freezing, or see if they still had a house. They left carrying backpacks and pulling suitcases or wagons down the footpath.
President Joe Biden on Friday declared a major disaster in the area, ordering federal aid be made available to those affected.
The wildfire broke out unusually late in the year, following an extremely dry autumn and amid a winter nearly devoid of snow until the overnight snowfall.
Scientists say climate change is making weather more extreme and wildfires more frequent and destructive.
Ninety per cent of Boulder County is in severe or extreme drought, and it hadn't seen substantial rainfall since mid-summer. Denver set a record for consecutive days without snow before it got a small storm on December 10, its last snowfall before the wildfires broke out.