A possible leak is being investigated at a US nuclear facility after radioactive material was found on a worker’s clothing.

The probe began after a contractor with Washington River Protection Solutions (WRPS), detected a spike in radiation levels on a device called a "crawler" that had been pulled out of a nuclear waste tank.

"Established decontamination procedures were followed, which involves removing the contaminated clothing. Further surveying the worker showed no contamination remained. No other workers were affected, and all members of the crew were cleared for normal duty," said WRPS spokesman Peter Bengtson.

The Double-Shell Tank AZ-101 contains 800,000 gallons of nuclear waste, according to the Washington Department of Ecology, which oversees the Hanford site.

Washington governor Jay Inslee called it a “serious situation”, and managers of the plant sent workers a message telling them to “secure ventilation in your building” and to “refrain from eating or drinking".

The discovery follows an incident last week, which forced hundreds of workers to “take cover”, after a tunnel in the nuclear finishing plant collapsed in Washington State.

The tunnel collapse had been found by workers on patrol, and while researchers did not find leaked or spilled radioactive materials, it nevertheless caused concern.

Several officials are calling for an investigation of the site, fearing additional leaks.

Maia Bellon, director of the Washington Department of Ecology, is requesting “an immediate investigation by US Dept of Energy into contamination [and] potential leak in a Hanford nuclear waste tank”.

Spokesperson Shaylyn Hynes said: "The US Department of Energy is continuing to monitor the situation at Hanford double-shell tank AZ-101. There is currently no sign of a leak from the tank into the environment. We are continuing to investigate to determine the source of contamination found on equipment late last week. Preparations are underway to conduct video inspections of the space between the inner and outer shells of the tank, known as the annulus, and those inspections are set to begin later this week.

"The worker who had contamination on his clothing last week has not experienced any skin contamination or signs of exposure that would cause negative health impacts. The Department is committed to ensuring the safety of its workforce, the public and the environment, and will continue to keep stakeholders apprised as more information becomes available."

Located in south-central Washington, the former plutonium production site was used to help develop the American nuclear arsenal 70 years ago.