Two people have been killed by the most destructive wildfire in Colorado history, law enforcement officials have said, as crews fought to keep the fierce, wind-whipped blaze from roaring into the outskirts of Colorado Springs.

El Paso County Sheriff Terry Maketa said on Thursday the bodies of two people had been recovered in the burn area of the so-called Black Forest Fire, which has destroyed at least 360 homes near the northeastern fringe of the state's second-largest city.

The blaze has ripped across more than 6,215 hectares of terrain northeast of Colorado Springs since it erupted on Tuesday, forcing some 38,000 people to flee the flames.

The two victims, who were not immediately identified, were found in the open garage of their home in a heavily wooded area, apparently overtaken by flames as they attempted to evacuate, Maketa said.

Maketa said that a person who spoke to the victims by phone said the pair reported seeing the glow of flames in the distance as they packed to leave. Forty minutes later, he said, a second witness spoke to them by phone.

"The person they were speaking with said he could hear popping and cracking in the background and they (the two people) advised they were leaving right now," Maketa said.

"We were truly hoping that we could get from day to day without coming across news like this," he said.

With the fire still burning out of control and driven by erratic, 48 kph winds that showed no sign of diminishing, officials on Thursday ordered mandatory evacuations of about 1,000 homes in the northern tip of Colorado Springs that were considered to be in imminent disaster.

"Load your family, and pets and GO NOW," the El Paso County Sheriff's Office said in a tweet. A voluntary evacuation order was issued for another 2,000 homes in Colorado Springs as embers drifted over the city.

Parched state

Firefighters have struggled to draw solid containment lines around the blaze, which along with several other major fires in the state underscored concerns that persistent drought could intensify this year's fire season in the western United States.

So far, flames from the Black Forest Fire have not damaged properties within the city limits of Colorado Springs. In addition to the 360 homes destroyed outside the city, 14 were damaged and the status of 79 others could not be determined.

More than 400 firefighters were battling the fire, assisted by water-dropping aircraft and 140 personnel from the Colorado National Guard. The Guard loaned three UH-60 Black Hawk helicopters carrying 500-gallon water buckets to the effort.

"We're not confident that if the winds changed and pushed the fire to any one of our boundaries that it could be held," Maketa said.

Last summer, the Waldo Canyon Fire destroyed nearly 350 homes in the city and surrounding areas.

Maketa said the Black Forest Fire, named for the community where it broke out, has now claimed more homes than the Waldo blaze, which was then considered the most destructive in state history. The Waldo fire killed an elderly couple and forced 35,000 people from their homes.