LUNA, N.M. >> Crews battling a massive wildfire in eastern Arizona for two weeks shifted their focus Monday to New Mexico, where they lit fires to stifle flare-ups that skipped along treetops threatening a small mountain town.

In the opposite corner of New Mexico, near the Colorado border, a wildfire that has forced hundreds of people from their homes more than doubled in size to an estimated 6,000 acres, after being fanned by high winds.

“We’re watching trees explode before our eyes. It’s horrendous,” said Barbara Riley, a schoolteacher and bed-and-breakfast owner in the northeastern New Mexico community of Raton.

A 20-mile section of the main north-south highway through New Mexico and Colorado remained closed due to the fire, causing hundreds of travelers to drive hours out of their way.

At the Wallow fire Monday in Arizona, crews worked furiously to protect the working-class mountain town of Luna, N.M., just across the border, after a successful weekend of no major fire growth.

Hundreds of firefighters worked alongside U.S. Highway 180 between Luna and the state line, hacking down brush and using chain saws to cut down trees. The other side of the road was blackened from the fires they set to clear a break.

Thick plumes of gray smoke swallowed the evening sun, turning it blood red above Luna, where the sky looked like a thunderstorm was brewing.

At Luna Lake in Arizona, just a few miles from the town of Luna, a steady stream of helicopters collected water and flew west to attack flames sending up thick, gray smoke from the pines. Fire officials said the flare-up was in the tree crowns, an ominous sign that the fire was gaining, but it was still several miles from Luna.

Earlier Monday, Catron County Undersheriff Ian Fletcher said he had not ordered the 200 or so residents of Luna to leave, but had a plan in case it was needed.

Fire spokesman Sean Johnson said the work crews have done clearing brush and setting their own fires to burn off fuel along the state line has so far spared Luna from the inferno.

“That’s what’s saved the town,” Johnson said. “The line is holding. There’s no fire in New Mexico that we haven’t set ourselves.”

Residents of two Arizona towns on the fire’s northern edge were allowed to go back home Sunday, and thousands streamed into Eagar and Springerville throughout the weekend and Monday. Crews have stopped its northern advance and are trying to corral its eastern push into New Mexico by burning a line in front of the fire that it can’t cross.

The wildfire near the New Mexico-Colorado border started Sunday on the west side of Interstate 25 and jumped to the east side later that day. Between 800 and 1,000 people were asked overnight to leave their homes northeast of Raton.

The fire prompted the closure of I-25 from Trinidad, Colo., to Raton, sending summer motorists on lengthy detours. Fire officials confirmed two structures have burned, but they could not say whether they were homes, businesses or outbuildings.

The blaze more than doubled in size in a matter of hours Monday, to about 9 square miles, as crews worked to protect evacuated homes and businesses.

Of the plume of smoke rising from the hills outside Raton, Mayor Neil Segotta said: “It looks like your worst nightmare.”

The Wallow fire, burning since May 29, had grown to 706 square miles, or more than 452,000 acres, by Monday. Containment increased from 10 percent Monday morning to 18 percent by night, Johnson said.

And officials continued to express optimism that their efforts were paying off.

“It’s getting better every day,” fire spokesman Kelly Wood said.

The blaze is the second largest in state history, although it has burned only 31 homes, four rental cabins and 36 outbuildings. The state’s largest fire, the 2002 Rodeo-Chediski, burned 732 square miles and destroyed 491 buildings.

Although about 7,000 residents of Eagar and Springerville were allowed to go home, about 2,700 others who live in several Arizona resort communities in the Apache-Sitgreaves National Forest remained under an evacuation order.

Fire officials said Monday they were working to make the picturesque hamlets of Alpine, Nutrioso and Greer safe for residents to go home, possibly later this week.

Greer, considered the jewel of eastern Arizona’s summer havens, lost more than 20 homes and a couple dozen outbuildings as flames moved into the valley last week. It includes lodges and hundreds of old and new cabins, including one owned by U.S. Sen. Jon Kyl, who was forced to evacuate on June 4.

Several other fires were burning around Arizona on Monday, including a huge blaze near the southeastern border town of Portal that has burned more than 232 square miles since May 8. It is about 50 percent contained. Another fire that broke out Sunday outside Sierra Vista near the Coronado National Memorial has forced evacuations.

In southern Colorado, a wildfire spread to about 1,000 acres and forced the evacuation of a church camp. Crews were attacking the blaze near Westcliffe from the air Monday. It broke out Sunday afternoon and spread quickly in dry conditions.

Meanwhile, in southeastern Colorado, crews are close to containing three large wildfires that broke out last week.