Three homes burned and dozens of others were evacuated Wednesday as a wind-whipped grassfire northwest of Idaho's capital city expanded to thousands of acres and threatened rural subdivisions. No injuries were reported.

Firefighting planes, water bucket-wielding helicopters and about 50 fire trucks, engines, water tenders, brush rigs and bulldozers were dispatched to the site about 15 miles northwest of Boise. More than 300 firefighters from multiple agencies combined to fight the blaze.

The three homes were destroyed, as was a barn, said Lynn Hightower, a Boise Fire Department spokeswoman.

The fire, which was reported early Wednesday afternoon, began burning as an electrical storm moved through the area north of the town of Eagle, near State Highway 16. Lightning is the likely culprit, said Mallory Eils, a Bureau of Land Management spokeswoman on the scene, adding firefighters were making good progress Wednesday evening.

"They're using the bulldozers to put a line in the ground, scraping down to bare dirt, making sure it's around all the last active portions of the fire," Eils said.

She said firefighters will be monitoring the blaze, estimated to have burned ground totaling about four square miles, into the night and Thursday morning.

This area's undulating sage- and cheatgrass-covered foothills have seen the arrival of several sprawling subdivisions in recent decades. Residents from evacuated homes were instructed to go to a nearby high school to wait out the flames.

"It looked like an inferno," one unidentified resident of an evacuated subdivision told KTVB-TV in Boise.

Hightower said at least 37 law enforcement agents from three agencies were going from home to home, warning residents.

"The deputies were responsible for checking dozens of homes, notifying homeowners about the approaching fire and getting those families out of the harm's way," she said.

The region's dry desert landscape, coupled with high winds, make southwestern Idaho prime territory for fast-moving wildfires, given the right conditions.

In August 2008, a fire just east of Boise killed one woman, destroyed 10 houses and damaged nine others. An equipment failure on Idaho Power Co. electricity lines ignited that fire.

A separate grassfire also was burning Wednesday in a remote area between Boise and Mountain Home in the southwestern Idaho desert.

Also, the National Interagency Fire Center reported that the Teapot Dome fire, some 10 miles east of Mountain Home, has expanded to 600 acres, but is about 60 percent contained.