US fire officials have evacuated 350 homes in Featherville as an unchecked forest fire bears down on the small town, 50 miles (80 km) east of Idaho state capital Boise.

"The smoke was really, really thick ... you could see across the street, but not much farther," Featherville fire spokesperson Lisa Machnik said during Monday's evacuation. "It's not a matter of if it will get here, but when."

According to Machnik, almost half the 1,120 available fire fighting personnel are in Featherville, implementing protective measures against the fire, which is expected to reach the town Wednesday.

National Forest Fire officials said the so-called Trinity Ridge Fire is the nation's highest priority wildfire. It has already engulfed 91,644 acres and is one of three large Idaho forest fires that that have each destroyed nearly 100,000 acres.

All three, the Trinity Ridge, Halstead and Mustang Complex fires, located in the central part of the state, are less than 7 percent contained. With a total of 42 fires burning statewide, Idaho officials say 2012 is the state's worst fire season in history.

Idaho, bordering Canada to the north, joins Colorado, Utah, Arizona and New Mexico as having its worst fire season in the past two years. In Colorado, more than 600 homes have gone up in flames in the High Park and Waldo Canyon fires in the past 90 days.

The northwest US, from Northern California and Washington state to the Dakotas, has entered its peak forest fire season, with record low moisture, high temperatures and extreme drought conditions creating maximum potential for burning.

What worries officials the most is that the unprecedented amount of fires may be unstoppable until Mother Nature intervenes.

"We may have to wait for rain or snow to put them out," said US Interagency Fire Center spokesperson Robyn Eroyles. "That may not be until mid October."

The Trinity Ridge is the only large fire threatening homes.

The Halstead Fire, which has engulfed 91,987 acres, is located 18-miles (30-km) northwest of Stanley, Idaho. It is only 5 percent contained and burning in a rugged area of the Salmon-Challis National Forest, taking advantage of large areas of beetle-killed trees to spread.

The Mustang Complex Fire, which has burned 89,859 acres, is located east of Lucky Ridge and was started by a half-dozen lightning strikes and is only 6 percent contained.

"They were both started by lightning," Eroyles said. "Mustang is in such steep, rugged terrain that we need to devise a strategy about how to fight the fires."

"The fuel condition is bad and there's a lot of heavy down timber. It could be burning a long time," she said.