Three people are missing after a wildfire tore through several Colorado towns, quickly destroying nearly 1,000 homes as part of the latest in a string of US natural disasters.

"We're very fortunate that we don't have a list of 100 missing. But unfortunately we do have three confirmed missing people," Boulder County Sheriff Joe Pelle told a press conference.

On Dec 31, 2021 firefighters walk near a home destroyed by a wildfire in Boulder County, Colorado
On Dec 31, 2021 firefighters walk near a home destroyed by a wildfire in Boulder County, Colorado AFP / Jason Connolly

At least 991 homes are thought to have been destroyed as the blaze raced through the towns of Superior and Louisville on Thursday, just outside the state's biggest city Denver, forcing tens of thousands of people to flee with little notice.

Shocking aerial footage showed whole streets as little more than piles of smoking ash, destruction that appeared almost total but somehow left a few homes oddly untouched.

Pelle said the search for the missing had been hampered by the destruction and snow.

Louie Delaware embraces his wife Judy as his daughter Elise embraces her fiance McGregor Ritter after returning to the remains of their home in Louisville, Colorado on December, 31, 2021
Louie Delaware embraces his wife Judy as his daughter Elise embraces her fiance McGregor Ritter after returning to the remains of their home in Louisville, Colorado on December, 31, 2021 AFP / Jason Connolly

"The structures where these folks would be are completely destroyed and covered with about eight inches (20 centimeters) of snow right now."

Investigators found no credible evidence to back earlier reports that downed power lines may have caused the fire, with Pelle stating that some residents may have been confused by downed telecom lines.

However, investigators have "executed a search warrant in one particular location" as part of an ongoing investigation that Pelle described as "very active" and comprising federal and state partners.

Debris lies scattered in the basement of a home destroyed by wildfire in unincorporated Boulder County, Colorado on December, 31, 2021
Debris lies scattered in the basement of a home destroyed by wildfire in unincorporated Boulder County, Colorado on December, 31, 2021 AFP / Jason Connolly

The fire, which was sparked in a tinder-dry landscape, was then fanned by winds gusting at more than 100 miles (160 kilometers) an hour on Thursday.

"This was a disaster in fast motion... over the course of half a day. Many families having minutes to get whatever they could -- their pets, their kids -- into the car and leave," Governor Jared Polis said, "just as in the blink of an eye."

At least 33,000 people in Superior and Louisville were told to flee, many doing so with little more than the clothes on their backs.

Pelle said he spoke to the granddaughter of one of the missing on Saturday morning.

"They're trying to find grandma. And we're trying to find grandma for her," he said. "But the conditions right now don't make that possible to do quickly."

While snowfall had helped extinguish the fire, it was a "hard thing for crime scenes, and recovery efforts and damage assessments," Pelle said.

The fire, which occurred just before the New Year's holiday, follows mid-December tornadoes in the state of Kentucky that left dozens dead and thousands of families in crisis mode ahead of Christmas.

Although fires are a natural part of the climate cycle and help to clear dead brush, their scale and intensity are increasing.

Scientists say a warming climate, chiefly caused by human activities such as the unchecked burning of fossil fuels, is altering weather patterns.