Tens of thousands of Americans nervously awaited word Thursday of whether their homes had been destroyed when a wildfire tore into the outskirts of this western US city.

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, forcing some 36,000 people to flee.

The fire, one of several blazing across the front range of the Rocky Mountains, has torched more than 18,500 acres (7,400 hectares), and reportedly destroyed some 300 homes, though no official figure has been given.

There have been no reports of deaths or injuries.

In a sign of the scale of the destruction, US President Barack Obama plans to visit the state on Friday and spoke with Colorado Governor John Hickenlooper and Colorado Springs Mayor Steve Bach on Wednesday.

Obama expressed concern about the destruction and "informed both that his thoughts and prayers are with responders and families impacted by these and other fires burning across the western United States," a statement said.

The High Park Fire, a blaze sparked by lightning some 60 miles northwest of Denver -- and described by the Denver Post as Colorado's second-largest in history -- has eaten through 87,284 acres but is now 75 percent contained.

Firefighters are also working to keep the Flagstaff Fire -- estimated at just over 200 acres -- away from the city of Boulder, home to the University of Colorado.

Several other fires are burning in other parts of the state -- famous for winter skiing and adventure sports -- including the Little Sand Fire, which was sparked by lightning on May 13 and has burned through 22,440 acres of land.

Among the areas threatened by the Waldo Canyon fire was the US Air Force Academy, which evacuated two housing areas a day before the scheduled arrival of 1,000 new cadets.

The Denver Post published an aerial photograph Wednesday that it said showed some 300 houses had been destroyed in the Mountain Shadows neighborhood within the limits of Colorado Springs, the state's second largest city.

Officials have declined to give a precise count, saying they have not been able to visit the charred areas because of the fire's intense heat.

Soaring temperatures have compounded the agony for teams battling the blaze, which is estimated to be only five percent contained.

Turbulent winds have prompted authorities to seek evacuations of up to 36,000 people, Hickenlooper told CNN Wednesday.

At a Red Cross evacuation center displaced residents -- many with nothing more than the clothes on their back -- nervously awaited word of whether their homes and belongings had been destroyed.

Artist Colin Gingrich, 38, said he managed to get all of his watercolor paintings out of his apartment but had to leave the acrylics behind. "I'll have to remember how they looked so I can do them over," he said.

Fire Incident Commander Rich Harvey told reporters Wednesday that there was concern the wind was pushing the flames toward Colorado Springs, which was already enveloped by a heavy plume of smoke.

"The wind is kicking up and it's causing us problems," Harvey said.

It was not immediately clear what sparked the Waldo Canyon Fire but Hickenlooper, who raced to the scene Tuesday, suggested it was not lightning.

"There's suspicion out there that we've got some idiot," he told CNN. "We're working as hard as we can to approach and get the real facts and not jump to conclusions."

The Federal Bureau of Investigation (FBI) said it was helping local law enforcement to determine whether the fires were caused by "criminal activity."

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

"It's just like the perfect storm for fires," Hickenlooper said.

Four US Defense Department C-130 aircraft were assisting local teams to contain the blazes, airlifting water and retardant.

As of Wednesday morning, they had carried out 23 air drops over the Waldo Canyon Fire and five over the Flagstaff Fire, a statement said. The National Guard has also been mobilized to help in the efforts.

The neighboring state of Utah is also combating a major fire, which burned through more than 6,000 acres of grassland in an area south of state capital Salt Lake City.

More than 8,400 people, 578 fire trucks and 79 helicopters have been deployed to tackle wildfires around the United States, the White House said.

Colorado is considered a swing state in the November presidential election, meaning that neither Obama nor his presumed Republican rival Mitt Romney can be guaranteed a victory there.