A 1,740-square-kilometre wildfire in eastern Arizona crept over the state border into New Mexico over the weekend, triggering a health alert in the neighbouring state about hazardous air quality.

New Mexico officials are warning residents about the throat-burning smoke spewing from a gigantic wildfire in eastern Arizona that has been blazing for several weeks.

Firefighters are now battling spot fires sprouting up in New Mexico and lighting their own fires to beat it back.

Health officials warned residents as far away as Albuquerque and Santa Fe about potential respiratory hazards, noting sensitive groups such as those with asthma, lung or heart disease, children, pregnant women and seniors should take extra precautions.

The forest fire remained largely uncontained and officials said the return of gusty southwesterly winds Saturday stoked the blaze where it had been just smouldering before.

Microscopic particles can lodge in lungs

Levels of tiny, sooty particles from the smoke in eastern Arizona were nearly 20 times the federal health standard on Saturday and Sunday could get even worse, said Mark Shaffer of the Arizona Department of Environmental Quality.

The microscopic particles, about 1/28th the width of a human hair, can get lodged in the lungs and cause serious health problems, both immediate and long-term, Shaffer said.

"Larger particles, you breathe in and you cough and it tends to get rid of it," he said, adding that the tiny particles get "very, very deep into your system and are very difficult to expel."

More than 30 homes have been destroyed since the fire began May 29, posing a potential danger to two major power lines that bring electricity from Arizona to West Texas as more than 3,200 firefighters fought to bring it under control. Containment regressed slightly to just 5 per cent, on the northeastern edge.

Nearly 10,000 people have been evacuated from the towns of Springerville and Eagar and from several other mountain communitiesin the forest, where officials said residents may be allowed back in soon, but also warned of lingering air pollution.

The fire is the second-largest in Arizona's history and could eclipse the 2002 Rodeo-Chediski fire in size, although only a fraction of the homes have burned. That blaze burned 1,895 square kilometres and destroyed 491 buildings.

Firefighters are battling another major wildfire in far southeastern Arizona, also near the New Mexico line. The so-called Horseshoe Two blaze burned through 546 square kilometres of brush and timber since it started in early May. The fire has destroyed 23 structures but caused no serious injuries. It was 45 per cent contained and fire officials hope to have it fully contained by late June.