HELENA, Mont. -- Crews and equipment from 34 states arrived Monday to help fight four massive wildfires that have destroyed a dozen homes in eastern Montana and forced ranchers to let their livestock loose as the blazes spread unhindered across roads, rivers and man-made fire lines.

The reinforcements come from states from Alaska to Florida. They were particularly needed Monday, as shifting winds threatened another run by the fires in a rural area south of the Missouri River that have burned a combined 353 square miles.

It's the largest complex of fires in a state with 18 blazes burning, which is more than twice as many as Alaska, the next highest state with eight, according to the National Interagency Fire Center.

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Many of the Montana fires were ignited by lightning strikes over the past week, and spread rapidly thanks to a heatwave and drought conditions.

The sudden rash of fires caused Gov. Steve Bullock to declare an emergency Sunday that will allow the state to use the National Guard in the firefighting efforts.

In eastern Montana, the Lodgepole Complex Fire, consisting of several fires, had collectively scorched an estimated 226,000 acres as of Monday, CBS affiliate KXLH-TV in Helena reports.

Rep. Greg Gianforte was in eastern Montana on Sunday for an update on the fires. "The most important thing right now is to put the fire out," he said, according to KXLH-TV. "Then we have to figure out how to help the county."

Cattle stand near the Bridge Coulee Fire, part of the Lodgepole Complex, east of the Musselshell River, north of Mosby, Mont., on July 21, 2017. Reuters

The eastern Montana fires have been burning since Wednesday through private farmland with scattered homes, along with a mix of rolling open land used for grazing and timber-choked river bottoms.

One of the fires jumped the Musselshell River and leapt over fire breaks cleared by bulldozers, frustrating crews that have contained just 5 percent of the fire complex.

The destroyed homes were discovered within the area ravaged by the largest blaze between the towns of Jordan and Winnett, east of the Musselshell River.

Another 50 homes in the area were under evacuation orders.

A heat-related injury caused a firefighter to be pulled from the line, fire information officer Tim Engrav said.

Livestock have likely died in the fires, but responders have not had a chance to make a tally. Ranchers were cutting fences to let their cattle out as the fire line spread toward their land.

Cattle are seen near the flames of the Lodgepole Complex fire in Garfield County, Mont., on July 21, 2017. BLM/Pete McFadden/Handout

"There's been a lot of scattering like that," Engrav said. "We know there is probably going to be some losses."

In the mountains near the Idaho border, another fire was threatening 50 homes and other structures after growing to 2 square miles.

The fire was burning near the town of Superior in Lolo National Forest, about 60 miles west of Missoula.

Elsewhere, people living near a wildfire in a rural area of northeast Washington state have been ordered to evacuate.

The wildfire had grown to about 350 acres and there was no containment.

A wildfire near a heavily populated area in Colorado may have been sparked by a grass mower.

Investigators are still looking into what sparked the fire south of Fort Collins, which temporarily triggered an evacuation south of Horsetooth Reservoir on Saturday.