LOS ANGELES: Hundreds of workers at a nuclear site in the US state of Washington were ordered to take cover on Tuesday after a tunnel filled with contaminated material collapsed near the facility.

Employees at the Hanford Site plant, located about 275 kilometres southeast of downtown Seattle, were sent an alert by management in early morning telling them to `secure ventilation` and refrain from `eating or drinking`.

The Hanford nuclear site was used to produce plutonium for the bomb that brought an end to World War IL Its last reactor closed down in 1987, but millionsof gallons of leftover waste are contained in tanks at the site.

A statement by the US Department of Energy said personnel at the facility were evacuated and workers in potentially affected areas had gone indoors.

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

It said it had activated an emergency operation at the plant shortly after an alert was declared.

There was speculation that road work near the tunnel caused it to collapse.-AFP