The defence ministry said the risk had become “unacceptable”, after the depot partially caved in, covering many of the explosives with fallen rock.

A report by the Federal Office for the Environment concluded last year that the 3,500 tonnes of ammunition and explosives stored in the underground site posed a bigger danger than was previously assumed.

In 1947 7,000 tonnes of explosives in the depot blew up, killing nine people.

Now authorities want to remove the remaining arms at the former underground depot at Mitholz - an operation that could take a decade to prepare, and then could force 170 residents of the village to leave their homes to facilitate the clearance.

"Depending on how the work develops, residents should expect the evacuation to last up to more than 10 years," the ministry said, adding that the explosives would not be removed until 2031 at the earliest.

It also said a major road passing through the village could be rerouted and a railway line would have to be covered.

There is also the possible Plan B of burying the ammunitions under more rock, but it is not the preferred option, with residents seeing it as leaving a “toxic gift for descendants”, according to project manager Hanspeter Aellig at a media conference on Tuesday.

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