Smoke from a massive Idaho wildfire posed a health risk to a small mountain town that was the staging area for firefighters battling the blaze, health officials said on Tuesday.

Government air monitors showed pollution levels peaked in the hazardous zone Monday night as the Mustang Complex fire, north of Salmon in east-central Idaho, poured thick smoke into a community that has coped with poor air for nearly seven weeks.

"I think we all have to consider it a crisis at this point," said Jim Vannoy, program manager for environmental health education and assessment with the Idaho Department of Health and Welfare.

The lightning-sparked blaze that has raged since late July is one of several large fires in the West.

Idaho's Mustang Complex in the Salmon-Challis National Forest grew to nearly 300,000 acres on Tuesday as firefighters braced to defend homes in two small communities. About 400 residences were ordered evacuated on Sunday.

In neighboring Washington state, 100 smaller wildfires from the Washington-Oregon line to just west of Spokane and north to the Canadian border charred 80,000 acres, threatening scores of homes, officials said.

In Idaho, relief from the smoke was not expected any time soon. The smoke contains noxious gases like carbon monoxide and fine particles that can drive deep into the lungs and aggravate or cause respiratory or heart ailments.

Public health experts said research is limited on the long-term effects of wildfire smoke because the exposure usually is concentrated in remote, sparsely populated areas.

"In general, the thoughts are that the health effects will be resolved because the events are, at most, weeks in duration," said Joel Kaufman, professor of environmental and occupational health at the University of Washington.

Janet Nelson, local emergency services coordinator, said she was fielding reports of children coughing to the point of vomiting, health workers complaining of fatigue and scores of people with persistent headaches.

"I have worries for the health of the community," she said.

County emergency managers provided residents with masks on Tuesday. Nelson said her office had dispensed nearly 300 masks and school officials urged students to wear them.

"I feel like I'm a smoker - and I don't smoke," said Kellen Miller, a 26-year-old science teacher, describing nights of disrupted sleep and work days made difficult by headaches.

In Washington state, about 2,500 firefighters, helped out by 150 minimum-security prison inmates, were able to hold most fires in the state at bay. State Department of Natural Resources spokesman Bryan Flint said shifting winds due on Thursday could cause problems.

The most threatening blaze, the Canyons Fire, a mile west of Wenatchee, merged with the Twin Peaks fire on Tuesday. It burned 1,200 acres and prompted evacuation of 150 homes.