The Energy Department on Tuesday warned of possible radioactive exposure at its nuclear weapons facility in Hanford, Wash., after a tunnel containing nuclear waste collapsed.

The agency sent out a notice advising Hanford residents about the possible risk. It also said employees have been told to shelter in place.

"There are concerns about subsidence in the soil covering railroad tunnels near a former chemical processing facility. The tunnels contain contaminated materials," said an earlier agency alert from the Hanford operations center.

A more recent department update stated that emergency first responders have arrived at the site, with the fire department reporting "there is no indication of a release of contamination at this point."

The collapse occurred at the tunnels next to the Plutonium Uranium Extraction Facility, also known as PUREX, and was "discovered during a routine surveillance of the area by workers."

The tunnels are hundreds of feet long, with about eight feet of soil covering them, the agency said. "The depth of the subsidence of soil appears to be into the tunnel."