More firefighters were called up on Tuesday to help fight a raging wildfire in the western US state of Colorado, which remains out of control and has claimed one life, officials said.

Up to 200 firefighters were ordered in to help reinforce the 400 already battling to contain the blaze northwest of Denver, along with aircraft, including five of the nine heavy air tankers available nationwide.

"There was some good progress made today with a lot of hard work by crews," said an update late Monday from the Larimer County Sheriff's Department.

"The fire is looking better tonight than last night.... There was a lot of air support today including a lot of water drops by the helicopters along both the south and northeast flanks of the fire," it said.

But the blaze remained zero percent contained, and had spread to cover 41,140 acres (16,650 hectares) by late in the day, compared to 39,000 acres (15,800 hectares) in the morning, and more than double the night before.

A spokesman confirmed the death of a 62-year-old woman, Linda Steadman, who had been reported missing and whose remains were found in the ashes of her burned-out home, authorities said.

The blaze, dubbed the High Park Fire, broke out early Saturday near Fort Collins, about 60 miles (100 kilometers) northwest of Denver.

By Monday seven helicopters, five Single Engine Air Tankers(SEATs), the five heavy air tankers and two other aircraft were involved in the operation, said the Sheriff's Department.

The Colorado National Guard also provided two Blackhawk helicopters for use today either for transport or bucket drops depending on the need.

"We have good reason to believe there are 100-plus structures that are damaged or destroyed. When I say structures, we don't know if they are homes, sheds or what," Larimer County Sheriff Justin Smith told reporters.

"Four hundred ground and engine crews are fighting the fire. We expect to have 500-600 working by the end of tomorrow," added the late evening update.

The cause of the fire has been confirmed as lightning.

In New Mexico, meanwhile, some 34,500 acres have been consumed in a fire also thought to be due to lightning, which has so far destroyed 35 structures, said the state fire information service in an online update.

"Higher humidity and lower wind speeds, combined with the arrival of additional personnel and equipment, provide an opportunity to make progress today," it said.