Louis Batides / Reuters Large plumes of smoke from a wildfire burning in the Black Forest stretch the horizon threatening homes northeast of Colorado Springs on Tuesday.

Wildfires fueled by hot, gusty winds were burning hundreds of acres and forcing evacuations Tuesday in three different parts of Colorado, a large part of which was under a red flag warning for extreme wildfire risk.

Fire agencies said their resources were being stretched critically thin as they tried to battle the fires simultaneously.

About 3,600 people had been evacuated from about 1,250 homes northeast of Colorado Springs after a smoky, fast-moving fire broke out at about 2 p.m. (4 p.m. ET) near Black Forest Regional Park, the El Paso County Sheriff's Office said. Residents of 300 more homes were asked to evacuate voluntarily.

No casualties were immediately reported, and Sheriff Terry Maketa said fewer than 10 homes were believed to have burned.

The National Weather Service issued a red flag warning for southeastern Colorado until 11 p.m. ET because of "critical fire weather conditions" — 95 degrees and dry, with strong winds.

"As you can tell, weather is not working with us," Maketa said.

Neither were some residents. Maketa said some who'd ignored earlier evacuation orders were now calling asking for help.

"Some have changed their minds," he said.

The fire was moving rapidly, and authorities had no immediate estimate of how many acres it covered. Maketa said the county was trying to muster all the state and federal resources it could, but with two other major fires burning in Colorado, it wasn't clear when reinforcements might arrive.

A fire jumped the Arkansas River near Cañon City and the historic Royal Gorge Bridge, spreading rapidly to cover about 3,000 acres by Tuesday evening. With containment pegged at 0 percent, about 200 people had already been evacuated, and about 800 more were being asked to leave.

Territorial State Prison in Cañon City was put on standby to evacuate its roughly 16,000 inmates if needed, authorities said.

Officials said the fire near Cañon City, Colo., could threaten the iconic Royal Gorge Bridge.

"It's certainly not out of the question that we'll be fighting this fire for another week," said Gregg Goodland, a Royal Gorge fire spokesman, who said an evacuation for Cañon City itself remained a possibility. "This fire is not going to go away any time soon, especially under the dry conditions."

A third fire, meanwhile, was burning in Rocky Mountain National Park after having been sparked by lightning Monday, NBC station KUSA of Denver reported. At least five trails in the park were closed by the fire, the size of which more than tripled, to 300 to 400 acres, in just a couple of hours Tuesday afternoon.

No structures were threatened in the park, the Forest Service said.

Parker Enix-Ross of NBC News contributed to this report.

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