LOS ALAMOS, N.M. (AP) – Authorities ordered Los Alamos evacuated Monday as a fast-growing and unpredictable wildfire bore down on the northern New Mexico town and its sprawling nuclear laboratory.

The blaze that began Sunday already had destroyed an unspecified number of houses south of the town, which is home to some 12,000 residents. It also forced the closure of the nation’s pre-eminent nuclear lab while stirring memories of a devastating blaze more than a decade ago that destroyed hundreds of homes and buildings in the area.

“The hair on the back of your neck goes up,” Los Alamos County fire chief Doug Tucker said of first seeing the fire in the Santa Fe National Forest on Sunday. “I saw that plume and I thought, `Oh my god here we go again.”’

Tucker said the blaze that grew to more than 68 square miles overnight was the most active fire he had seen in his career, forcing residents near Cochiti Mesa and Las Conchas to flee with “nothing but the shirts on their back.”

Traffic on Trinity Drive, one of the main roads out of Los Alamos, was bumper-to-bumper Monday afternoon as residents followed orders to leave. Authorities said about 2,500 of the town’s residents left under earlier an earlier voluntary evacuation.

“We’re just hoping for the best,” Vivian Levy, a resident since the 1970s said as she packed her car and her animals – again.

“Last time, I just walked out of my house and said goodbye, and that it was going to be OK,” she said before breaking down in tears. “I’m doing the same thing this time. It’s going to be OK. I’m prepared to say goodbye.”

Sam Kendericks said he knew the blaze was going to be bad when he first saw the plume Sunday.

“I was going to the hardware store and I did a U-turn as soon as I saw the plume come over the mountain. I told my wife to start packing. We were here 10 years ago. We had 20 minutes last time. So this time we’re ready,” he said. “

The fire has the potential to double or triple in size, Tucker said, and firefighters had no idea which direction the 60 mph-plus winds would take it.

“We are preparing for the fire to go in any direction,” Tucker said.

On Monday afternoon, the flames were just across the road from the southern edge of the famed northern New Mexico lab, where scientists developed and tested the first atomic bomb during World War II. The lab activated its emergency operations center overnight and cut natural gas to some areas overnight as a precaution. Officials said all hazardous and radioactive materials were being protected.

In 2009, the U.S. Department of Energy’s inspector general issued a report that said Los Alamos County firefighters weren’t sufficiently trained to handle the unique fires they could face with hazardous or radioactive materials at LANL.

Lab and fire department officials at the time said the report focused too much on past problems and not enough on what had been done to resolve them. Some problems also were noted in previous reports.

On Monday, lab and fire officials said they were confident that if the flames reached lab property they would be able to protect its sensitive facilities.

“We’re in a much better place than we were 11 years ago,” said Rich Marquez, executive director of the lab, noting the lab has thinned out potential fire hazards and has enacted a number of emergency protocols.

“Our day to day activity is about appropriate stewardship of those resources. We take precautions just in our normal existence and the way we plan, the way we manage materials like that. We assume the worst.”

The lab, which employs about 15,000 people, covers more than 36 square miles and includes about 2,000 buildings at nearly four dozen sites or “technical areas.” Those include research facilities as well as waste disposal sites. Some lab facilities, including the administration building, are in the community of Los Alamos while others are several miles away from the town.

Greg Mello, with the anti-nuclear watchdog Los Alamos Study Group, said the group doesn’t have enough information “to formulate any views on safety at this point.”

“It is important to remind ourselves that the site has natural hazards ... and Murphy’s Law is still about the best enforced law in the state,” he said.

The blaze also was threatening Frijoles Canyon, which is home to a number of sacred native American archaeological sites. Also threatened, Tucker said, was the recently restored Bandelier National Monument.

At least 30 structures had burned south of Los Alamos overnight, but Tucker said it was unclear exactly how many homes had been destroyed.

The blaze started on private land about 12 miles southwest of Los Alamos and quickly grew. Flames and smoke could be seen from the outskirts of Albuquerque, about 80 miles away.

The fire was eerily similar to one of the most destructive fires in New Mexico history. That fire, the Cerro Grande, burned some 47,000 acres – 73 square miles – in May 2000 and caused more than $1 billion in property damage. About 400 homes and 100 buildings on lab property were destroyed in that fire.

That blaze also raised concerns about toxic runoff and radioactive smoke, although lab spokesman Kevin Roark said no contaminants were released in the Cerro Grande fire.

Environmental specialists from the lab were mobilized and monitoring air quality on Monday, he said, but the main concern was smoke.

Meanwhile, the biggest blaze in Arizona history was 82 percent contained after burning through 538,000 acres in the White Mountains in northeast Arizona. The fire started May 29 and has destroyed 32 homes. It’s believed to have been caused by a campfire.

And in Colorado, about 100 firefighters are battling a wildfire that broke out in a canyon northwest of Boulder.

Fire officials have put 340 homeowners on standby to evacuate. No structures are immediately threatened by the fire.

In southern Colorado, hot, windy weather has caused a wildfire that’s been burning since June 12 to spread. The Duckett fire grew by about 400 acres over the weekend but it’s not threatening any homes. Most the growth has been in a steep, rugged terrain in the Sangre de Cristo Mountains.

The fire is burning on 7-square miles and is 80 percent contained.

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Associated Press writers Jeri Clausing in Albuquerque and Barry Massy in Santa Fe contributed to this report.