* Hundreds of homes menaced by cluster of lightning-caused blazes

* Smoke and ash prompts health advisory for residents in two counties

By Laura Zuckerman

SALMON, Idaho, Sept 4 (Reuters) - A cluster of lightning-sparked wildfires roaring through national forests in Idaho threatened hundreds of homes on Tuesday, prompting evacuations from several small towns and sending clouds of ash cascading over the region.

The so-called Mustang Complex blaze has devoured more than 240,000 acres since originating as several smaller fires that erupted from thunderstorms in late July in remote stretches of the Salmon-Challis National Forest, then merged during the ensuing weeks.

The fire crept closer on Tuesday to two small towns near the Montana border - North Fork and Gibbonsville - just north of the eastern Idaho city of Salmon, menacing about 250 homes, authorities said. Officials have advised some residents to flee, while others were placed on standby for possible evacuation.

Thick smoke and ash belched from the Mustang fire, and from a separate lightning-caused blaze that has scorched over 130,000 acres in the Salmon-Challis, enveloped the region, prompting state health officials to issue an air pollution alert.

In North Fork, firefighters scrambled trying to determine how best to protect a high-end resort, the 100 Acre Wood Lodge, from advancing flames.

"We thought we were in good shape. Now we're not so sure," said Jon Cummings, co-owner of the resort, after area property owners were warned to be ready to flee at a moment's notice.

Fire information officer Tom Hegele said fire crews were still in a defensive stance and were ready to fall back if flames appeared ready to overtake their positions.

"If this thing suddenly jumps and runs, we're not going to risk human life," he said.

Jeff Hill, the chief executive officer of Steele Memorial Hospital in Salmon, said his facility and a sister clinic were reporting a rise in the number of patients complaining of breathing difficulties due to the fire, especially among those with asthma.

About 65 miles to the west, a third fire dubbed the Mcguire Complex blaze was threatening more than 300 structures, mostly homes and cabins, in the towns of Orogrande and Dixie in the Nez Perce National Forest, prompting evacuations there since last Tuesday, authorities said.

The Mcguire fire has raged largely unchecked over 16,000 acres of rugged, densely forested terrain since unleashed on Aug. 27 by a lightning strike. The blaze was so fierce that only specially trained U.S. Forest Service "hotshot" teams have been assigned to the fire so far.

A force of nearly 1,000 firefighters was battling the sprawling Mustang Complex, by far the largest of five major wildfires being fought across Idaho on Tuesday, according to the National Interagency Fire Center in Boise.

One of those, the Trinity Ridge Fire, came close to swallowing the small resort village of Featherville in the Boise National Forest of south-central Idaho about two weeks ago. But a prolonged, intense effort by firefighters saved the town. That blaze, which charred more than 145,000 acres, has since been largely contained.

Earlier in August, a U.S. Forest Service firefighter was killed when a tree fell on top of her in north-central Idaho, bringing to 12 the number of wild-land firefighters who have lost their lives in the line of duty nationwide this year. (Writing by Steve Gorman; Editing by Cynthia Johnston and Stacey Joyce)

Earlier on HuffPost:

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  • A house is engulfed in flames near Highway 48 and HW 38 junction east of Drumright, Okla., on Saturday, Aug 4, 2012. Emergency management officials have ordered evacuations of homes in several areas as wildfires burn across the state. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • Flames burn near Highway 48 and HW 38 junction east of Drumright, Okla., on Saturday, Aug. 4, 2012. Emergency management officials have ordered evacuations of homes in several areas as wildfires burn across the state. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • A home burns during a large wildfire Friday, Aug. 3, 2012 in Luther, Okla. A wildfire whipped by gusty, southerly winds swept through rural woodlands north and south of Oklahoma City on Friday, burning several homes as firefighters struggled to contain it in 113-degree heat. (AP Photo/The Oklahoman, Bryan Terry)

  • A house is engulfed in flames near Highway 48 and HW 38 junction east of Drumright, Okla., Saturday, Aug 4, 2012. While residents of one Oklahoma town sifted through their charred belongings Saturday to salvage what they could after a roaring wildfire that may have been deliberately set, residents in two other towns were being ordered to evacuate their homes. (AP Photo/Tulsa World Tom Gilbert)

  • Kellyville firefighter Levi Stephens fights a grassfire in Kellyville, Okla., near West 151st and the Turner Turnpike, Saturday, Aug 4, 2012. Emergency management officials have ordered evacuations of homes in several areas as wildfires burn across the state. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • Kellyville firefighter Levi Stephens fights a grassfire in Kellyville, Okla., near West 151st and the Turner Turnpike on Saturday, Aug 4, 2012. Emergency management officials have ordered evacuations of homes in several areas as wildfires burn across the state. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • Structures are engulfed in flames near Highway 48 and HW 38 junction east of Drumright, Okla., on Saturday, Aug 4, 2012. Emergency management officials have ordered evacuations of homes in several areas as wildfires burn across the state. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • Rebecca Kolar stands at the entrance to the three bedroom, brick home at 908 S. Dogwood Street where she and her husband, Douglas lived with their two children for 13 years before fire destroyed it, Saturday, Aug. 4, 2012 in Luther, Okla. While residents of one Oklahoma town sifted through their charred belongings Saturday to salvage what they could after a roaring wildfire that may have been deliberately set, residents in two other towns were being ordered to evacuate their homes. The fire near Luther, which is about 25 miles northeast of Oklahoma City, destroyed nearly five dozen homes and other buildings before firefighters were able to gain some measure of control Saturday.(AP Photo/The Oklahoman, Jim Beckel) TABLOIDS OUT

  • Tracy Streeper hugs five year-old grandson Jesse, as they stand on the north side of Streeper's destroyed home, Saturday, Aug. 4, 2012 in Luther, Okla. While residents of one Oklahoma town sifted through their charred belongings Saturday to salvage what they could after a roaring wildfire that may have been deliberately set, residents in two other towns were being ordered to evacuate their homes. The fire near Luther, which is about 25 miles northeast of Oklahoma City, destroyed nearly five dozen homes and other buildings before firefighters were able to gain some measure of control Saturday.(AP Photo/The Oklahoman, Jim Beckel) TABLOIDS OUT

  • A house is engulfed in flames near Highway 48 and HW 38 junction east of Drumright, Okla., on Saturday, Aug 4, 2012. Emergency management officials have ordered evacuations of homes in several areas as wildfires burn across the state. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • Victoria Landavazo holds youngest child, Axel, 1 year old, while wiping tears after arriving with other members of her family to see for the first time what the wildfire had done to their home, Saturday, Aug. 4, 2012 in Luther, Okla. While residents of one Oklahoma town sifted through their charred belongings Saturday to salvage what they could after a roaring wildfire that may have been deliberately set, residents in two other towns were being ordered to evacuate their homes. The fire near Luther, which is about 25 miles northeast of Oklahoma City, destroyed nearly five dozen homes and other buildings before firefighters were able to gain some measure of control Saturday.(AP Photo/The Oklahoman, Jim Beckel) TABLOIDS OUT

  • Flames and smoke threaten structures near Highway 48 and HW 38 junction east of Drumright, Okla. Emergency management officials have ordered evacuations of homes in several areas as wildfires burn across the state. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • Area firefighters fight a grass fire east of 120th at Cemetery Road on Friday, Aug. 3, 2012, east of Norman, Okla. A wildfire stirred by high winds sweeping through rural woodlands just south of the Oklahoma City area has set at a number of homes on fire. (AP Photo/The Oklahoman, Steve Sisney)

  • A helicopter drops water on a large grass fire east of 120th near Cemetery Road on Friday, Aug. 3, 2012, east of Norman, Okla. A wildfire stirred by high winds sweeping through rural woodlands just south of the Oklahoma City area has set at a number of homes on fire. (AP Photo/The Oklahoman, Steve Sisney)

  • Flames leap into the air as area firefighters fight a wildfire on Cemetery Road east of 120th on Friday, Aug. 3, 2012, east of Norman, Okla. A wildfire stirred by high winds sweeping through rural woodlands just south of the Oklahoma City area has set at a number of homes on fire. (AP Photo/The Oklahoman, Steve Sisney)

  • Ruth Hood hugs her dog Punky while waiting a gas station at SE 108th and Hwy 9 after evacuating her home near SE 132nd and Hwy 9 as a wildfire burns through Cleveland County near Norman, Okla., Friday, Aug. 3, 2012. A wildfire stirred by high winds sweeping through rural woodlands just south of the Oklahoma City area has set at a number of homes on fire. (AP Photo/The Oklahoman, Nate Billings)

  • Vin Bayne pours water for his pets while waiting at a gas station at Hwy 9 and SE 108 Ave. after evacuating his home as a wildfire burns through Cleveland County near Norman, Okla., Friday, Aug. 3, 2012. A wildfire stirred by high winds sweeping through rural woodlands just south of the Oklahoma City area has set at a number of homes on fire. (AP Photo/The Oklahoman, Nate Billings)

  • From left, Gayland Cannon, Eugene Hacker and Ron Ross wait at a gas station at SE108 and Hwy 9 after evacuating their homes in the area of SE 132nd and Cedar Lane as a wildfire burns through Cleveland County near Norman, Okla., Friday, Aug. 3, 2012. A wildfire stirred by high winds sweeping through rural woodlands just south of the Oklahoma City area has set at a number of homes on fire. (AP Photo/The Oklahoman, Nate Billings)

  • A mobile home burns at South Cedar and South 8th St., during a large wildfire, Friday, Aug. 3, 2012 in Luther, Okla. A wildfire whipped by gusty, southerly winds swept through rural woodlands north and south of Oklahoma City on Friday, burning several homes as firefighters struggled to contain it in 113-degree heat. (AP Photo/The Oklahoman, Sarah Phipps)

  • A smoke surrounds home during a large wildfire Friday, Aug. 3, 2012 in Luther, Okla. A wildfire whipped by gusty, southerly winds swept through rural woodlands north and south of Oklahoma City on Friday, burning several homes as firefighters struggled to contain it in 113-degree heat. (AP Photo/The Oklahoman, Sarah Phipps)

  • A home burns during a large wildfire Friday, Aug. 3, 2012 in Luther, Okla. A wildfire whipped by gusty, southerly winds swept through rural woodlands north and south of Oklahoma City on Friday, burning several homes as firefighters struggled to contain it in 113-degree heat. (AP Photo/The Oklahoman, Sarah Phipps)

  • Bill Ragle walks past the remains of his home that was destroyed by a wildfire in Mannford, Okla., Sunday Aug. 5, 2012. (AP Photo/Tulsa World Mike Simons)

  • In this Saturday, Aug. 4, 2012 photo, flames engulf a house near Highway 48 and HW 38 junction east of Drumright, Okla. The Oklahoma Department of Emergency Services says no injuries have been reported. (AP Photo/Tulsa World, Tom Gilbert)

  • Casey Strahan, lower left, and Logan Renner, 17, look at the reamins of their homes, Saturday, Aug. 4, 2012 in Luther, Okla. While residents of one Oklahoma town sifted through their charred belongings Saturday to salvage what they could after a roaring wildfire that may have been deliberately set, residents in two other towns were being ordered to evacuate their homes. The fire near Luther, which is about 25 miles northeast of Oklahoma City, destroyed nearly five dozen homes and other buildings before firefighters were able to gain some measure of control Saturday.(AP Photo/The Oklahoman, Jim Beckel) TABLOIDS OUT