DENVER (REUTERS) - Crews battling a deadly wildfire that is the most destructive on record in Colorado have contained almost half of the 6,070ha blaze that has incinerated nearly 500 homes outside Colorado Springs, authorities said on Saturday.

Cooler temperatures, calmer winds and a rainstorm that moved over the burn area on Friday allowed fire managers to increase the containment of the fire to 45 per cent from 30 per cent the day before.

"Last night, there was no growth and no more structures lost," incident commander Rich Harvey of the US Forest Service told a news conference.

But the number of homes confirmed destroyed by the so-called Black Forest Fire jumped to 473 overnight as assessment crews combed through areas that have cooled, El Paso County Sheriff Terry Maketa said.

Mr Maketa said the bulk of the homes were lost in the first 24 hours of the blaze, and voiced optimism the threat from the fire was diminishing.

"I think we're getting the upper hand," Mr Maketa said, adding that when he toured the area, it "looked like a nuclear bomb went off." Fueled by tinder-dry vegetation and fanned by high winds, the blaze erupted on Tuesday in a wooded area northeast of Colorado Springs.

Flames roared out of control for two days, charring a 62 sq km swath through rolling hills on the outskirts of Colorado's second-largest city.

Two people were found dead inside the garage of a home that was reduced to ashes when flames ripped through the area.

The sheriff said the cause of the fire was under investigation, but he believed it was caused by humans, because there were no lightning strikes in the area that could have sparked the blaze.

At one point, some 38,000 people were under evacuation orders. But authorities have lifted evacuation orders in some areas as the threat of the fire spreading has eased.

Next week, some displaced residents will be allowed back into neighborhoods that have been deemed safe, police said. The sheriff's office said unauthorized people found in restricted areas would be criminally charged.

More than 1,000 local, state and federal firefighters are attacking the fire from the ground and air, Harvey said, and firefighting costs have exceeded US$3.5 million.