Media playback is unsupported on your device Media caption Doug Tucker, fire chief: "We're doing our best to keep it off the lab"

One of the top nuclear weapons research facilities in the US will remain closed until Thursday as fire fighters battle a wildfire raging at its boundary.

Only "essential-duties" staff at Los Alamos National Laboratory will be permitted on site on Wednesday.

Officials at the New Mexico facility have said they detected "no off-site releases of contamination".

The town outside the laboratory in the state of New Mexico was evacuated on Monday as the fire raged nearby.

Officials said the nuclear facilities faced "no immediate threat" but warned of damage to houses.

The lab, opened during World War II, led the development of the atomic bomb.

Possible toxic plume

By midday on Tuesday, the Las Conchas fire had grown to 93 sq miles (241 sq km), burning through forests, canyons, and mesas, fuelled by dry timber and powered by strong winds.

Los Alamos blaze from space NASA space shot of Los Alamos fire

The blaze was said to be as close as 50ft (15m) away from the grounds of the lab on Tuesday afternoon, raising fears it could reach a cache of 30,000 drums, each containing 55 gallons (208 litres) of plutonium-contaminated waste.

The fire had reached the lab's southwestern boundary and leapt a state road onto the land, burning roughly an acre, state fire officials said.

"The concern is that these drums will get so hot that they'll burst," Joni Arends, executive director of the Concerned Citizens for Nuclear Safety, told the Associated Press news agency.

"That would put this toxic material into the plume," she added.

But officials said there was very little risk of the fire actually reaching the lab's facilities and that workers were standing near the waste drums to coat them with fire-resistant foam if the blaze got too close.

Authorities said the fire could triple in size in the coming days, the Albuquerque Journal reported.

The fire blew enormous plumes of black smoke over the town of Los Alamos and forced the evacuation of the entire community, which has a population of roughly 12,000.

"We are throwing absolutely everything at this that we got," Democratic Senator Tom Udall of New Mexico said.

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.