Emergency crews battled a fire at a New Mexico site where the US government seals away its low-grade nuclear waste, including plutonium-contaminated clothing and tools.
Six people were treated for smoke inhalation after a truck carrying salt caught fire at the waste plant near Carlsbad on Wednesday.
All employees were evacuated from the underground site and none of the radioactive waste was affected, plant officials said.
Authorities said they were not sure what caused the blaze.
The Waste Isolation Pilot plant is the only deep geological nuclear repository in the United States. It takes waste from Los Alamos National Laboratory and defence projects, and buries it in rooms cut from underground salt beds.
Officials said the fire occurred on a truck in the facility's north mine, the Carlsbad Current-Argus newspaper reported. Nuclear waste was stored in the south mine, officials said.
Fire suppression systems and rescue teams were immediately activated, and all waste handling operations were suspended, officials said.
A spokeswoman answering an emergency line on Wednesday evening said it was unclear if the fire was still burning or when the site might reopen.
The New Mexico facility receives 17 to 19 shipments each week from nuclear sites around the country.