Hundreds more firefighters were ordered to fight the biggest wildfire in a decade in Colorado, as federal agencies scrambled to help tackle blazes in several western US states.

More than 500 firefighters were attacking the blaze and plans were to have as many as 700 to 800 by Wednesday, said officials. Aircraft, including five of the nine heavy air tankers available nationwide, were being used.

"We thought we were around five percent (containment). My hope for today is that we should be around 10 percent, weather dependent," federal fire incident commander Bill Hahnanberg told reporters.

But a mid-morning update warned: "Weather conditions will be warmer and drier today with shifting winds which will cause concern for firefighters," adding that 100 fire engines were expected to be involved by Wednesday.

By Tuesday, 14 helicopters including three Blackhawks from the National Guard were helping the operation, along with five of the nine Single Engine Air Tankers (SEATs) available nationwide, and five heavy air tankers, it said.

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

The blaze has mushroomed to 43,000 acres (17,200 hectares), making it the third largest in Colorado history, having more than doubled to 39,000 acres from Sunday to Monday alone.

The fire has claimed one life, a 62-year-old woman whose remains were found in the ashes of her burnt-out cabin. The cause of the fire has been confirmed as lightning.

In neighboring New Mexico, meanwhile, firefighters said better weather conditions Monday had enabled them to make progress on containing a fire that has ravaged more than 36,000 acres.

Nearly 1,000 crew were dealing with the New Mexico blaze, which was now 30 percent contained, according to an update on the website.

"Yesterday's break in the weather allowed firefighters to make significant progress," it said.

"However, firefighters are not lulled into complacency, because the fire is still active and there is strong potential for extreme fire behavior. Crews will use yesterday's progress as a basis for continued progress today."

The Department of Homeland Security meanwhile said it was working "closely" with emergency services tackling wildfires in a number of western states also including Arizona, California, Utah and Wyoming.

In all 19 active large fires were burning in nine states, "including one of the largest wildfires in New Mexico history and one of the largest wildfires in Colorado history," it said.

In all, some 4,500 extra firefighters have been dispatched by federal agencies, which are also providing emergency funding to help states cope with the costs of tackling mass blazes.

"We continue to support our state, local, and tribal partners as they work to contain and suppress the wildfires burning in the West," said Secretary of Agriculture Tom Vilsack.

Secretary of the Interior Ken Salazar added: "We remain vigilant and continue to do all we can to ensure the safety of all firefighters in this challenging wildlife season."