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Hundreds of workers were told to take cover at the Hanford Nuclear Reservation after a tunnel full of highly contaminated materials collapsed Tuesday. But officials say no radiation was released, and no workers were hurt.

Officials say a collapsed patch of ground above the tunnel was larger than first believed. The U.S. Department of Energy said the collapse covered about 400 square feet (37.1 square meters) instead of the 16 square feet (1.4 square meters) first reported.

Hundreds of workers were told to go into a "take cover" position after the tunnel in a plutonium-uranium extraction (PUREX) plant collapsed. 

The agency says the rail tunnels are made of wood and concrete and are hundreds of feet long, with about eight feet (2.4 meters) of soil covering them. The U.S. Department of Energy says the incident caused the soil above the tunnel to sink between 2 and 4 feet (half to 1.2 meters).

They were originally constructed to hold rail cars that were loaded with contaminated equipment.

Eight rail cars are in the tunnel that collapsed, but it feeds into a longer tunnel that contains 28 loaded rail cars. The tunnel collapsed near where the two tunnels join.

The tunnels were sealed in the mid-1990s, and are checked periodically. During routine surveillance, the agency said it discovered a 20-foot wide hole in the roof of one of the tunnels.

"I would underscore this is confined to a small area of the Hanford site," Destry Henderson, deputy news manager for the Hanford Joint Information Center, told NBC News. "The facility does have radiological contamination right now, but there is no indication of a radiological release," Henderson said.

A manager sent a message to all personnel telling them to "secure ventilation in your building" and "refrain from eating or drinking."

A source said "take cover" status was expanded to the entire site at 10:35 a.m. The source also said that crews doing road work nearby may have created enough vibration to cause the collapse and that Vit Plant employees were in cover mode as well.

Robots were being used to determine possible air contamination.

Responding agencies include the U.S. Department of Energy; Richland, West Richland, and Kennewick city fire and police; Benton, Franklin, and Grant County Fire and police officials; Washington State Patrol; and Oregon and Washington state officials.

The Statesman Journal reports the Oregon Department of Energy has activated its emergency operation center in response to the Hanford emergency, which is 35 miles away from Oregon.

Washington Gov. Jay Inslee said the Department of Energy and The White House reached out to his office after the incident.

"I think anytime there's a failure of your expected containment, it's a concern," said Inslee.

He said the state is monitoring the air quality independently from federal authorities.

Related: Hanford tunnel collapse is a 'warning,' state lawmaker says

Hanford, which is roughly half the size of Rhode Island, spent decades making plutonium for the nation's nuclear weapons arsenal.

KING 5 Investigative Reporter Susannah Frame is covering this story. Follow her online at @SFrameK5 for the latest.

The Associated Press contributed to this report.