Employees were evacuated after an emergency alert was declared at a nuclear site in Hanford, Washington on Tuesday.

The Hanford Site said in a release that employees have been evacuated and “workers in potentially affected areas of the Hanford Site have gone indoors.”

“There are concerns about subsidence in the soil covering railroad tunnels near a former chemical processing facility,” the site said. “The tunnels contain contaminated materials.”

Local NBC affiliate KING reported that the tunnel contained radioactive transports for fuel rods.

KING reporter Susannah Frame reported that managers told employees to “secure ventilation” and “refrain from eating or drinking,” though whether there was any contamination remains unclear.

HANFORD EMERGENCY: Hundreds of workers are in "take cover"-must stay inside buildings after a tunnel collapse,. possible contamination — Susannah Frame (@SFrameK5) May 9, 2017

HANFORD Source: Vit Plant employees in take cover mode as well. — Susannah Frame (@SFrameK5) May 9, 2017

HANFORD NEW: Managers just sent this alert to employees. pic.twitter.com/A0mNu4oJbp — Susannah Frame (@SFrameK5) May 9, 2017

Hanford Source: "This is the biggest deal I've seen at Hanford in my 35 years here." — Susannah Frame (@SFrameK5) May 9, 2017

Hanford Source: Crews were doing road work near plutonium finishing plant. May have caused enough vibration to collapse tunnel. — Susannah Frame (@SFrameK5) May 9, 2017

It is not known yet if radioactive particles were released into the air from the tunnel collapse. Hanford workers taking cover as precaution — Susannah Frame (@SFrameK5) May 9, 2017

The tunnel that collapsed at Hanford is full of highly contaminated materials such as hot, radioactive trains that transported fuel rods — Susannah Frame (@SFrameK5) May 9, 2017

Highly contaminated items were stored in the tunnel that has collapsed at Hanford. @HanfordC calls this "a crisis." — Susannah Frame (@SFrameK5) May 9, 2017

Photo of massive plutonium finishing plant at Hanford. Tunnel that collapsed led to this building. pic.twitter.com/UG0hmXC78z — Susannah Frame (@SFrameK5) May 9, 2017

Emergency personnel standing by at Hanford. pic.twitter.com/zPBLb40Gzb — Susannah Frame (@SFrameK5) May 9, 2017

Other first responders standing by at Hanford, waiting to hear if they can move in closer. pic.twitter.com/uFTZPmkKcj — Susannah Frame (@SFrameK5) May 9, 2017

The dark area underneath the tall orange flag is the collapse site – a hole left by the tunnel collapse. pic.twitter.com/7fvqsRimhC — Susannah Frame (@SFrameK5) May 9, 2017