A fast-growing wildfire in southern Colorado has destroyed structures and forced the evacuation of more than 150 homes, officials said.

The fire was reported before dawn Monday some 25 miles southwest of Pueblo, the Custer County Emergency Management Office said.

And by Monday evening it had mushroomed to 21 square miles, according to El Paso County sheriff's spokeswoman Gail Perez.

The fire sent up large plumes of smoke, which led to a health advisory for people living as far east as Pueblo.

"We have confirmed four structures lost — one home and three other structures were lost on the Junkins Park Loop near where we believe the origin of the fire was," Custer County Sheriff Shannon Byerly told the Pueblo Chieftain.

U.S. Forest Service spokeswoman Dawn Sanchez told the newspaper that 156 homes were under a mandatory evacuation notice, while residents of another 140 were told to be ready to leave.

Firefighters from throughout the state headed to the blaze to assist crews from Custer and Pueblo counties. About 80 personnel were on the scene, and three air tankers were deployed.

But officials said high wind gusts had been grounding water-dropping aircraft.

The cause of the fire is unknown. But a stretch of dry, warm weather has raised the fire danger in much of Colorado, especially on windy days.

Officials said evacuations could be called for the small town of Beulah, which was evacuated by another wildfire earlier this month. That fire is believed to have been started by a state-operated excavator working in a ditch, possibly by creating a spark.

To the north, firefighters contained more than 50 percent of a 14-acre wildfire in Pike National Forest about 10 miles northwest of Colorado Springs. No structures were damaged.

Oscar Martinez, a district ranger with the U.S. Forest Service, said he hoped crews could fully contain the fire on Tuesday.

The fire was reported Monday afternoon near Rampart Reservoir. Its cause was unknown.