A firefighter works to combat the Hermits Peak and Calf Canyon wildfire, near Las Vegas, New Mexico. Reuters

US Rep. Teresa Leger Fernandez announced the presidential disaster declaration during an evening briefing by the US Forest Service about efforts to contain the sprawling wildfire in northeastern New Mexico, which has fanned out across 250 square miles (647 square kilometres) of high alpine forest and grasslands at the southern tip of the Rocky Mountains.

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"It will help us do that rebuilding and it will help us with the expenses and the hardship that people are facing right now,” the congresswoman said. "We're glad it happened this quickly.”

Fire bosses said they are seizing upon an interlude of relatively calm and cool weather to keep the fire from pushing any closer to the small New Mexico city of Las Vegas and other villages scattered along the fire’s shifting fronts. Airplanes and helicopters dropped slurries of red fire retardant from the sky, as ground crews cleared timber and brush to starve the fire along crucial fronts.

US President Joe Biden speaks during an event. File photo

Bulldozers for days have been scraping fire lines on the outskirts of Las Vegas, population 13,000, while crews have been conducting burns to clear adjacent vegetation. Aircraft dropped more fire retardant as a second line of defense along a ridge just west of town in preparation for intense winds expected over the weekend.

An estimated 15,500 homes in outlying areas and in the valleys of the Sangre de Cristo Mountains that border Las Vegas have been affected by mandatory evacuations. The tally of homes destroyed by the fire stands around 170.

The president's disaster declaration releases emergency funds to recovery efforts in three counties in northeastern New Mexico where fires still rage, as well as portions of southern New Mexico where wind-driven blazes killed two people and destroyed over 200 homes in mid-April.

A firefighter conducts a prescribed burn to combat the Hermits Peak and Calf Canyon wildfires. Reuters

The aid includes grants for temporary housing and home repairs, low-cost loans to cover uninsured property losses and other relief programs for individuals and businesses, a statement from the White House said.

Local law enforcement officials acknowledged the physical and emotion toll of prolonged evacuations. Las Vegas Police Chief Antonio Salazar said his officers would provide "burglary patrols” of evacuated areas and help maintain order at a local Walmart as people line up to purchase supplies.

"Repopulation, that's one thing we're very interested in,” San Miguel County Sheriff Chris Lopez said. "Everybody wants to get back home.”

Dan Pearson, a fire behavior specialist with the federal government, said weather forecasters are anticipating two days of relatively light winds before the return of strong spring gales.

A plane drops water to combat the Hermits Peak and Calf Canyon wildfires, near Las Vegas, New Mexico. Reuters

"Our prayers are working because we've had advantageous winds throughout the fire area today,” he said. "We'll take advantage of this fact over the next few days. ... What we can do is build resilient pockets."

The fire was contained across just 20% of its perimeter. Its flames on Wednesday were about a mile (1.6 kilometers) away from Las Vegas, where schools were closed as residents braced for possible evacuation.

Officials at Los Alamos National Laboratory were warily tracking another wildfire that crept Wednesday within about 5 miles (8 kilometers) of facilities at the U.S. national defense laboratory based in Los Alamos.

The Hermits Peak and Calf Canyon wildfire burns near Las Vegas, New Mexico, US, on Wednesday. Reuters

Fire crews worked to widen a road that stands between the fire and Los Alamos while clearing out underbrush and treating the area with fire retardant.

Wildfires have become a year-round threat in the drought-stricken West - moving faster and burning hotter than ever due to climate change, scientists and fire experts say. Fire officials also point to overgrown areas where vegetation can worsen wildfire conditions.

Nationally, the National Interagency Fire Center reported Wednesday that a dozen uncontained large fires have burned about 436 square miles (1,129 square kilometers) in five states.