Nearby residents have expressed concern about potential contamination if flames reach barrels stored outside.
But officials are confident the fire will not reach the drums and they say dangerous materials are safely stored.
The town outside Los Alamos National Laboratory was evacuated on Monday.
The laboratory has been closed since then and is not expected to open until Friday at the earliest, officials said.
The Las Conchas fire has now burned 110 sq miles (284.9 sq km), fuelled by dry timber and powered by strong winds. Smoke from the blaze can be seen as far away as Albuquerque 60 miles (100km) away.
"Everything is just so dry and ready to burn," Los Alamos County Fire Chief Doug Tucker told the Associated Press news agency."We need some rain. Snow would be nice," added Mr Tucker, whose department is responsible for protecting the lab.
On Wednesday, there were expected to be between 600 to 800 firefighters tackling the blaze, an official told the Albuquerque Journal, adding that the number could climb as high as 1,000.
Air National Guard members from Colorado, California and North Carolina have also flown in to help local crews battle the fire near the lab, which remains closed to all but essential staff.
The Environmental Protection Agency has deployed air monitors and aircraft that can monitor radiation levels, amid fears the blaze could reach a cache of 30,000 drums, each containing 55 gallons (208 litres) of plutonium-contaminated waste.
Fire managers said foam could be sprayed on the barrels containing the radioactive materials to ensure they were not damaged by fire, a procedure which would only be carried out as a last resort.Nearing the labOn Monday, the fire saw the evacuation of the town of Los Alamos, which has a population of roughly 12,000.
The facility, which opened during World War II, led the development of the atomic bomb.
On Tuesday evening, the wildfire was just across the road from the southern edge of the Los Alamos lab, roughly 50ft (15m) from the site's grounds.
The laboratory employs about 15,000 people, sprawls more than 36 square miles (93 sq km) and includes about 2,000 buildings over about four dozen sites.
The wildfire has destroyed 30 structures south and west of Los Alamos.
The south-western US has been stricken by giant wildfires this year, with millions of acres scorched in New Mexico, Arizona and Texas.
To the west of New Mexico, the largest wildfire in the history of the state of Arizona has been burning for nearly a month.
