ALBUQUERQUE, N.M. -- A massive wildfire that has burned more than 265 square miles in the Gila National Forest has become the largest fire in New Mexico history, fire officials confirmed Wednesday.

The erratic blaze grew overnight to more than 170,000 acres, surpassing a blaze last year that burned 156,593 acres in Los Conchas and threatened the Los Alamos National Laboratory, the nation's premier nuclear facility.

The Gila forest fire is also the largest currently burning in the country. It formed last week when two lightning-sparked blazes merged in an isolated mountainous area in southwestern New Mexico, where it has destroyed about a dozen homes and prompted evacuations of nearby towns and health alerts for some of the state's largest cities.

Fire information officer Jerry Perry said about 1,200 firefighters from around the state were battling the growing blaze, but that they continue to face low humidity and shifting winds in their efforts.

"We still facing adverse weather conditions that are posing a challenge," Perry said. "We're doing a lot of burnout operations and yesterday we had to deal with a lot of spot fires."

The fire has not been contained, and officials worry that shifting winds and dryness related to the state's record drought may cause the blaze to grow even more.

The blaze so far has threatened few communities and was burning away from many of New Mexico's largest towns and cities. But state officials issued air quality alerts for cities as far as Albuquerque, nearly 170 miles away, and Santa Fe last weekend, and Perry said parts of southern New Mexico could expect to see smoke from the fire.

The two lightning-sparked fires that have burned for about two weeks merged amid strong winds to form the giant blaze, which has destroyed 12 cabins and seven small outbuildings. Windy conditions forced crews to the sidelines last week as the fire rapidly spread in an isolated area and charred homes in the community of Willow Creek, which remains under evacuation.