A wildfire that was raging near the Los Alamos National Laboratory in northern New Mexico posed no threat to nuclear materials at a dumpsite near the facility, authorities said Monday.

The Las Conchas fire, which started Sunday in the Jemez Mountains, about 19 km west of the town of Los Alamos, forced the closure of the lab, where scientists developed the first atomic bomb during World War II, lab officials said.

They said the offshoot of the fire was safely extinguished, and no contamination had been released, according to The Los Angeles Times.

Lab spokesman Steve Sandoval declined to confirm whether there were any drums on the property. But he acknowledged that low-level waste was at times put in drums and regularly taken from the lab to the Waste Isolation Pilot Project site in Carlsbad, New Mexico.

Sandoval said the fire was "quite a bit away" from that storage area, but he could not say what would happen if drums containing such waste were to burn.

"Unfortunately, I cannot answer that question other than to say that the material is well protected. And the lab, knowing that it works with hazardous and nuclear materials, takes great pains to make sure it is protected and locked in concrete steel vaults. And the fire poses very little threat to them," he said.

The anti-nuclear watchdog group, Concerned Citizens for Nuclear Safety, said the fire appeared to be about 5.6 km from the dumpsite, where as many as 30,000 drums, each with a capacity to hold 55 gallons of plutonium-contaminated waste, were stored in tents.

The group said the drums were awaiting transport to a low-level radiation dumpsite in southern New Mexico.

By early Monday, the fire had burned 50,000 acres (about 20,250 hectares) and destroyed 30 structures south and west of Los Alamos, making the evacuation of thousands of residents in the affected area necessary,The Los Angeles Times said.

The Las Conchas wildfire has the potential to double or triple in size, said Los Alamos County Fire Chief Doug Tucker, and firefighters have no idea which direction the winds, with a speed of more than 96 km an hour, will take it.

"We are preparing for the fire to go in any direction," he said.

In May 2000, a similar devastating blaze, known as the Cerro Grande fire, destroyed hundreds of homes and buildings in the nearby town of Cerro Grande, posing a threat to the weapons lab.

"We feel like we are in much better shape to deal with a wildfire than in the Cerro Grande era," Sandoval said. "It was an eye-opener for us, to say the least."