A shocked US President Barack Obama on Friday toured "heartbroken" Colorado neighborhoods torched by rampaging wildfires, viewing charred homes and cars melted by intense heat.

Crews were meanwhile searching for human remains in the ashes of homes destroyed by the Waldo Canyon Fire, which blazed into the outskirts of the state's second largest city Colorado Springs earlier this week.

The inferno destroyed at least 346 houses, forced some 36,000 residents to evacuate, and left at least one person dead, according to officials. It is still threatening some 20,000 homes and 160 commercial buildings.

Obama saw the smoke from nearby fires as he flew into Colorado Springs aboard Air Force One, then inspected some of the devastation and praised the "courage and determination and professionalism" of firefighters.

"They are genuine heroes," Obama said, after he visited a neighborhood where fires had struck indiscriminately, leaving some homes in ruins and others intact.

"You have a house that's cinders. Next to it, it's untouched," said Obama, who saw homes that had been turned into blackened ruins and several vehicles melted down to the frames. A smell of burnt wood hung in the air.

"This community is obviously heartbroken," Obama said, praising coordination between state and federal governments as they faced "enormous" devastation.

"We have been putting everything we have in trying to deal with what is one of the worst fires we have seen in Colorado."

Ahead of his visit, Obama issued a disaster declaration that releases federal emergency funds.

Late Thursday, Colorado Springs police chief Peter Carey announced the first casualty of the blaze, saying a body had been found in a burned-out house and that another person was missing at the same address.

Police spokeswoman Barbara Miller said the pair were believed to be husband and wife.

Officials fear others could have perished in the blaze that started Saturday, and raged out of control on Tuesday and Wednesday whipped up by high winds.

"We've gotten calls from people who say they haven't heard from people," said Miller.

The fire, which has scorched some 16,750 acres (6,700 hectares), is just 15 percent contained.

Several other blazes across the mountainous western US state were straining firefighting resources.

"The focus for today is to hold what we've got, improve the lines that we have in place, use aerial assets as necessary to support the troops on the ground," fire incident commander Rich Harvey told reporters.

The plan is to bring in more heavy equipment where possible "to further enhance our ability to put muscle down on the ground in front of this fire and keep it in its containment lines," Harvey said.

Some 33 crews were fighting the blazes with 76 engines and 11 bulldozers. Three helicopters had dropped 384,205 gallons of water.

Officials in Colorado Springs met privately on Thursday night with distressed evacuees -- many of whom fled with no time to collect their belongings.

"You never think it's going to happen to you," Rebekah Largent told reporters after leaving the meeting.

Her husband Byron said residents looked at lists of homes street-by-street.

"If your address wasn't there, that meant it (the house) was intact. And so you just look at the paper and you see destroyed, destroyed, destroyed, and you see one damaged and then destroyed, destroyed, destroyed," he said.

The Waldo Canyon blaze forced the evacuation of the nearby US Air Force Academy, where cadets joined fire crews in protecting their barracks and other buildings as the fire swallowed 10 acres of the academy's land.

Summer wildfires are common in the mountains of arid Colorado but rarely burst into residential areas, as the Waldo Canyon Fire did earlier this week. It is not yet known what sparked the blaze.

Record high temperatures, extremely low humidity and wind gusts of up to 60 miles (100 kilometers) an hour have fueled fires across the American West, where an unusually mild and dry winter left widespread tinder-like conditions.

The separate High Park fire -- sparked by lightning in a more remote area northwest of Denver -- is the second biggest in the state's history.

It destroyed 257 homes and ate through 87,284 acres but is now 75 percent contained, county officials said.

AFP Photo/Robyn Beck