Viennese historian Burkhart List, 62, says he has acquired documents from old Wehrmacht archives that report a mass shipment of the Hatvany collection to two subterranean galleries, measuring 6,000 by 4,500 feet, in the Erzgebirge Mountains.

With the permission of the mayor of nearby Deutschkatherinenberg, Hans-Peter Haustein, he deployed a neutron generator inside the mountain to probe for the secret chambers.  

The device revealed that, 180 feet down, there are workings detailed on no maps and they appear to be man-made, not natural.

Mr List said: 'In the winter of 1944 - 1945 the records indicate that a mysterious transport arrived here from Budapest that was coded top secret.

'One of the photos [above] yielded up by the archives was of the Sonnenhaus, a large building directly in front of the Fortuna mine where I believe the art is stored.

'It shows a large contingent of SS. There was no military or logical state purpose for them to be here on a secret mission, unless it was to deliver the artwork into chambers which, climactically, are ideal for the storage of art.'

So far the explorations have yielded only a Schmeisser machine gun, a Nazi gas mask, plastic explosive detonators and a safe deposit key.