Hundreds of workers at a nuclear site in Washington state were ordered to take cover Tuesday after a tunnel containing rail cars laden with nuclear waste caved in – but there were no reports of a radioactive leak, officials said.

Workers in one building were evacuated in Hanford, while others farther away were ordered to hunker down and turn off ventilation systems after minor damage was discovered in a tunnel, a federal official told Reuters.

The US Department of Energy said it activated its emergency protocol at the Hanford Nuclear Reservation in the small community in south-central Washington, the Washington Post reported.

Authorities detected no release of radiation and no workers were injured, said Randy Bradbury, a spokesman for the Washington state Department of Ecology.

Local media earlier reported that the tunnel had collapsed but a US Energy Department spokeswoman said that was incorrect.

“There is evidence of a small sunken area of soil that covers the tunnel, but no collapse,” said the spokeswoman, who declined to identify herself, citing agency policy.

The accident occurred at the Plutonium Uranium Extraction Facility, known PUREX, located in the middle of the sprawling reservation, which is about half the size of Rhode Island, NBC affiliate KING reported.

The Energy Department said responders reported that soil had “subsided” in an area about 4 feet by 4 feet over one of the tunnels, The Washington Post reported.

“The subsidence of soil was discovered during a routine surveillance of the area by workers,” the department said in a statement.

A source told KING that crews doing road work may have created enough vibration to cause the damage.

The tunnel was full of highly contaminated materials such as hot radioactive trains that transport fuel rods.

“The facility does have radiological contamination right now but there is no indication of a radiological release,” Destry Henderson, deputy news manager for the Hanford Joint Information Center, told the NBC affiliate.

Gov. Jay Inslee said he appreciated that the White House also reached out to his office to alert him about the incident.

“This is a serious situation, and ensuring the safety of the workers and the community is the top priority,” he said in a statement. “We will continue to monitor this situation and assist the federal government in its response.”

Hanford stores about 56 million gallons of nuclear waste, most in 177 underground tanks – some dating back to World War II and leaking — until it can be treated for permanent disposal, KING reported.

Ground was broken at Hanford in 2002 for a $17 billion vitrification plant to separate much of the waste into high- and low-level radioactive material.

“Vitrification is accomplished by mixing waste from Hanford’s underground tanks with glass-forming materials in high-temperature melters,” the Vit Plant says on its website.

“As the materials are heated to 2,100 degrees Fahrenheit, the waste is incorporated into the molten glass. This ‘liquid glass’ is poured into stainless steel canisters to cool,” according to the site. “Once cooled, the now-solid vitrified waste within the canisters can be disposed of permanently and safely.”

After the highly radioactive waste is placed in glass logs, it would be shipped to a national repository proposed for Yucca Mountain in Nevada.

Plutonium production ended at the site in 1980 and the cleanup program began in 1989.

The mostly decommissioned site made the plutonium for most of the US nuclear arsenal, including the bomb dropped on Nagasaki.

The complex has been a subject of conflict between state and local authorities, including a lawsuit over worker safety and cleanup delays.

With Post wires