The Colorado blaze shrouded the state capital, Denver, some 60 miles (100 km) away in smoke on Tuesday.
A woman has died in the blaze, which has burned about 43,000 acres (68 sq miles) and is still growing.
A huge fire is also burning in New Mexico – one of a total of 19 fires in nine drought-stricken western states.
The Larimer County Sheriff’s Office said on Monday that one person had died in Colorado, after investigators found remains in a home that had been burned in the fire.
Although the remains have not been conclusively identified, the family of Linda Steadman, 62, has issued a statement saying she died in a cabin that she loved.
They reported her missing after the fire started on Saturday, sheriff’s officials said.
President Barack Obama called the Colorado governor to offer federal personnel, equipment and emergency grants – but was unable to reach his New Mexico counterpart due to poor reception in the fire zone, the Associated Press reported.
The High Park Fire – as it has been dubbed – is still growing, with only 5% contained, reported a national incident information website.
The same website says 30% of the 36,000-acre (56-sq-mile) Little Bear Fire in New Mexico has been contained.
About 118 structures have been damaged or destroyed by the blaze in Colorado – believed to have been started by lightning – and hundreds of people were forced to evacuate, officials say.
Some 600 firefighters are on the scene and up to 200 more are expected.
Additional resources have had to be called in as state and federal authorities rushed to tackle the blaze.
The US Forest Service said on Monday it would contract one air tanker from Alaska and four from Canada to add to the aircraft already combating the fire. Two more air tankers were also being mobilized in California.
Five of the forest service’s 13 tankers have already been deployed to the scene, a spokesman said.
Congressmen from Colorado said in a letter to the forest service that the need for more aircraft was “dire”.
But incident commander Bill Hahnenberg told the Associated Press: “We are a very high priority nationally. We can get all the resources we want and need.”
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