Mauthausen-GusenWikimedia commons

A filmmaker discovered a network of tunnels and bunkers in Austria that is being touted as a gigantic secret Nazi weapons factory where a nuclear bomb may have been developed.

Austrian documentary filmmaker Andreas Sulzer found the 75-acre complex just outside the small town of St. Georgen an der Gusen, near Linz. This site is not far from the Bergkristall factory, where the Messerschmitt Me 262 -- the first operational jet-powered fighter -- was invented.

Sulzer noticed that an Austrian physicist who was recruited by the Nazis had mentioned about the subterranean site in his diary.

It was built by slave labourers who lived in the nearby Mauthausen-Gusen concentration camp.

The exact location of this Nazi factory was determined with the help of intelligence reports and radiation tests that revealed that the radioactivity levels at the site were higher than normal.

It is being suspected that the head of Schutzstaffel (SS) and Hitler's right-hand man Heinrich Himmler oversaw the development of the weapon of mass destruction. Experts say that the complex was the "biggest secret weapons production facility of the Third Reich".

Rainer Karlsch, a historian working who worked with Sulzer, said: "The SS leadership aspired to create a combination of missiles and weapons of mass destruction. They wanted to equip the A4 [a variant of the V-2] missile, or more advanced rockets, with poison gas, radioactive material or nuclear warheads," Mirror reports.

Sulzer told The Times: "This was a gigantic industrial complex."

The site was very well-hidden. Bulldozing equipment were required to cut away massive granite plates that the Nazis had used to hide the entrance shaft in 1945.

The explorers used ground penetrating radar to ascertain how large the facility was.

The complex is believed to be linked to the B8 Bergkristall underground factory that produced the Messerschmitt Me 262. This invention posed a brief threat to the allied air force towards the end of the war.

Trying to figure out what purpose this facility really served, Sulzer went on to get a crack team of historians to find further evidence of scientists working on the secret project.

Lastweek, Sulzer's excavation was halted by the local authorities who said that Sulzer would require a permit to continue his research on historic sites.

"Prisoners from concentration camps across Europe were handpicked for their special skills — physicists, chemists or other experts — to work on this monstrous project and we owe it to the victims to finally open the site and reveal the truth," Sulzer told the Sunday Times, Daily Mail reports.