LOS ALAMOS, New Mexico -- UPDATE 8:38 PM EDT -- New Mexico fire managers scrambled on Tuesday to reinforce ground crews battling for a third day against a fierce blaze roaring out of control at the edge of one of the nation's top nuclear weapons production centers.

Flames from the Las Conchas fire near the Los Alamos National Laboratory, a nuclear weapons facility with over 20,000 barrels of plutonium-contaminated waste, June 28, 2011. REUTERS/Craig Fritz The fire's leading edge burned to within a few miles of a dump site where some 20,000 barrels of plutonium-contaminated waste like clothing and equipment is stored on the grounds of the Los Alamos National Laboratory, fire officials said.

Officials for the government-run lab said the stored waste is considered low-level radioactive material and remains a safe distance from the fire in an area cleared of trees and other vegetation.

Carl Beard, director of operations for the lab, said there has been no release of radioactive or hazardous materials into the environment and there was no immediate threat to public safety, "even in these extreme conditions."

Authorities have for now suspended routine removal of the waste drums for shipment to a permanent underground disposal site in southern New Mexico, said Los Alamos County Fire Chief Douglas Tucker.

"Because of the fire, they are not moving any of that. It is safer where it is," he said.

The fire, believed to have been ignited Sunday by a fallen power line, has consumed nearly 61,000 acres of thick pine woodlands in the Santa Fe National Forest, which surrounds the lab complex and adjacent town of Los Alamos on three sides.

Tucker said he feared the so-called Las Conchas Fire, whipped by high, rapidly shifting winds, could soon double or triple in size. The blaze remained listed as at zero percent containment and burning largely unchecked in its third day.

"I seriously believe it could go to 100,000 acres," Tucker told reporters at a news briefing on Tuesday. "We have fire all around the lab. It's a road away."

A small offshoot of the blaze jumped State Highway 4 onto the lab grounds on Monday, burning about an acre of property before it was extinguished about two hours later.

More than 300 firefighters, backed up by several water-dropping helicopters, battled the blaze on Tuesday, as fire managers scurried to bring in additional ground crews.

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"We've been putting in orders to get as many firefighters here as we can," fire information officer Vanessa Delgado said. "We're trying to get them in as fast as we can."

Lab officials also called in teams late Monday to monitor air quality, with high-volume air samplers ready to deploy. Hundreds of National Guard troops have been dispatched to back up law enforcement in the area.

Both the town of Los Alamos, home to about 10,000 residents, and the laboratory, with a work force of about 12,000 people, were evacuated on Monday, and the lab will remain closed at least through Wednesday, officials said.

Situated on a hilltop 35 miles northwest of Santa Fe, the lab property covers 36 square miles and includes about 2,000 buildings, none of which has yet burned.

Established during World War Two as part of the top-secret Manhattan Project to build the first atomic bomb, it remains one of the leading nuclear arms manufacturing facilities in the United States.

John Witham, a spokesman for the anti-nuclear watchdog group Nuclear Watch New Mexico, said it is the only place in the country that produces plutonium pits that are carried in the core of nuclear bombs.

Three metric tons of highly radioactive weapons-grade plutonium is stored in concrete and steel vaults in the basement floor of a building near the center of the complex, with an air-containment system surrounding it.

Lab officials said the storage structures were fire safe.

Nuclear Watch New Mexico said on its website its greatest concern was for the 20,000 55-gallon sealed drums of plutonium-tainted waste stored at one corner of the complex, some stacked in the open on asphalt, some in tents, some buried underground.

Fire officials say if the blaze did manage to reach the area, they would use fire-retardant foam to douse the flames.

The watchdog group said it also was concerned about trace amounts of uranium that might remain scattered over an area in the path of the fire from decades of experimental explosions conducted on the site.

Lab officials say the facility overall is well-protected and note it survived a May 2000 wildfire that claimed some buildings and did more than $1 billion in damage.

The Las Conchas Fire has also destroyed about 30 structures southwest of the town of Los Alamos.

One major focus for firefighters has been to keep flames out of two heavily forested canyons in the area, at least one of which runs directly into town.

Writing by Steve Gorman; Editing by Jerry Norton