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 today.

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.

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.