Nearly 1,000 homes were destroyed and hundreds damaged as the blazes hit two towns in Boulder County in the US state.

For those who escaped the flames, heavy snowfall has compounded the misery.

US President Joe Biden has declared the scene a national disaster, freeing up federal funds to assist affected people and businesses in recovery efforts.

Three people were initially reported missing but one has been been accounted for, Boulder County Sheriff Joe Pelle said on Sunday.

The cause of the fire is still under investigation but Mr Pelle said authorities were pursuing a number of tips and had executed a search warrant at "one particular location", without providing further details.

After visiting some of the damaged neighbourhoods, Colorado Governor Jared Polis said: "I know this is a hard time in your life if you've lost everything or you don't even know what you lost.

"A few days ago you were celebrating Christmas at home and hanging your stockings and now home and hearth have been destroyed."

Winter grassland fires are rare in Colorado, but experts have warned similar events will be more common in the coming years as climate change warms the planet.

Professor Jonathan Overpeck, a climate scientist at the University of Michigan, said: "These fires are different from most of the fires we've been seeing across the West, in the sense that they're grass fires and they're occurring in the winter.

"Ultimately, things are going to continue to get worse unless we stop climate change."

The blazes burned through at least 9.4 square miles on Thursday and firefighters eventually brought it under control on New Year's Eve.

The fires had been fanned by winds of up to 105mph that helped flames leap to new ground.

Tens of thousands of people were ordered to flee, many escaping through thick smoke as the fires approached.

As the remains of properties were still smouldering on New Year's Day, the snow began to fall.

Families have been returning to their neighbourhoods to find burnt-out shells of their homes.

When resident Cathy Glaab returned to her property, she found it 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," Ms Glaab said through tears. "So many memories."

Red Cross shelter volunteers have been distributing electric heaters to residents as officials struggle to restore gas and electricity.

A historic drought and heatwaves have made wildfires harder to fight in the area, with 90% of Boulder County in severe or extreme drought having seen no substantial rainfall since mid-summer.

Extreme weather has also been taking hold in other parts of the US, with heavy snowfall disrupting road travel in the Pacific Northwest to California, and intense thunderstorms across the south damaging homes and buildings in Alabama.