Tens of thousands of people in the Denver area watched and waited nervously Wednesday as firefighters raced to battle a massive wildfire that continued to surge out of control toward their homes.
The fire has burned 90,000 acres in the foothills southwest of Denver since it began Saturday. But it has not grown much since Tuesday, giving fire crews a chance to go on the offensive for the first time in more than 24 hours.
About 450 firefighters marched toward the fire as plumes of billowing smoke rose to 20,000 feet, concealing the rolling hills between Denver and Colorado Springs.
The fire covers more than 135 square miles and has destroyed at least 21 homes.
Another 2,500 homes are threatened, and up to 40,000 people have been warned in the past three days that they may have to flee. Most of the activity Wednesday, however, was on the fire's southern flanks, away from the city.
"The fire itself is not going to threaten Denver," Gov. Bill Owens told The Associated Press. But, he added, "the smoke sure is."
The smoke has eased in the Denver area in the past two days, but it is still obscuring the city's postcard view of the Rockies. Some residents have swept gray flakes of ash off their vehicles, porches and plants daily. Others have sought medical help.
Valerie Miller, 49, who lives in southeastern Denver, was in her yard when the haze arrived Sunday.
"I thought that the solar eclipse had come a day early for some reason," she said. "When I started to smell the smoke I knew it was more serious than that."
She added: "I keep having to pull out my contacts because they burn from the ash in the air. It's not easy to drive this way."
William Allstetter of the city's National Jewish Medical and Research Center said patients suffering from asthma, emphysema and chronic bronchitis were complaining of more symptoms.
"We've also got a lot of phone calls," he said. "Many of the callers are feeling worse, a lot of them are worried."
State health officials have advised those with respiratory ailments to exercise indoors.
Authorities initially suspected the fire was started by a campfire, but investigators said Wednesday they were unsure of its origin other than that it was human-caused. It has moved slowly to the northeast, creeping within about 35 miles of the city limits.
The flames are much closer to small hamlets and subdivisions about 55 miles southwest of Denver. More than 5,400 people remained out of their homes Wednesday, primarily in mountain towns near the fire's origin. A small crowd gathered along a highway near Florissant, watching the smoke billow above.
Among them was Garry Helgestad, 55, who was forced to leave his home Tuesday. He and other evacuees cheered as slurry planes zoomed overhead.
"Come on, buddy!" he yelled, thrusting his fist in the air. "Get 'em!"
Ground crews worked to build lines around the fire as planes and helicopters dropped flame retardant and water. But rain isn't forecast until at least Friday, and fire managers worried that the wind might pick up.
"We're still dealing with a wind-driven fire, and some terrain issues. The winds are switching around," U.S. Forest Service spokeswoman Barb Masinton said.
Forest Service regional forester Rick Cables said he was worried because the fire season hasn't really begun in Colorado, which is under a drought emergency.
"We're way early," Cables said. He said more slurry has been used in the state since mid-April than was used in all of 2000 — a bad fire season in Colorado.
Joe Allbaugh, the head of the Federal Emergency Management Agency, toured fire sites with the governor Wednesday.
"The Hayman fire is the worst fire I've ever seen in my life," he said. "If astronauts are watching it from the space shuttle, you've got to know it's huge."
Other fires are burning across the state, including a 10,600-acre blaze that destroyed 28 homes near Glenwood Springs, about 150 miles west of Denver.
In southwestern Colorado, a 9,300-acre fire burning out of control north of Durango threatened 60 homes. La Plata County officials said most residents had left voluntarily.
The Associated Press contributed to this report.