Visitors walk through the entrance gate of the Auschwitz concentration camp in Oswiecim, southern Poland, in 2005. Polish police say the infamous iron sign over the gate was stolen early Friday morning. (Herbert Knosowski, File/Associated Press)

The iron sign bearing the Nazi slogan "Arbeit Macht Frei" (Work Shall Set You Free) that spanned the main entrance to the former Auschwitz death camp was stolen before dawn on Friday, Polish police said.

Museum guards at the Auschwitz concentration camp memorial alerted police at 5 a.m. local time on Friday after they noticed the sign was missing. The thieves appear to have unscrewed the sign on one side and torn it off on the other side, said police spokeswoman Katarzyna Padlo.

Museum spokesman Pawel Sawicki called the theft at the infamous labour camp, where over one million people died or were executed, a "desecration" and said he was shocked the tragic history of the site did not stop the thieves.

Police have launched an intensive investigation at the vast former death camp, where the ruins of watchtowers, barracks and gas chambers still stand in varying states of disrepair, a reminder of the atrocities inflicted by Nazi Germany on Jews, Poles, Roma and others during the Second World War.

Theft desecrates 'world memory'

An exact replica of the sign — made when restoration work was being done on the original — was immediately hung in place of the missing sign. Non-Jewish Polish inmates made the original sign in Auschwitz in 1940. The slogan was also used at the entrances to other Nazi death camps, including Dachau and Sachsenhausen.

Poland's Chief Rabbi Michael Schudrich condemned the theft, saying whoever has done it "has desecrated world memory."

"Auschwitz has to stand intact because without it, we are without the world's greatest reminder — physical reminder — of what we are capable of doing to each other," Schudrich said.

Between 1940 and 1945, more than one million people, mostly Jews, were killed or died of starvation and disease while carrying out forced labour at the camp, which the Nazis built in occupied Poland.

Today the site serves as one of the main tourist draws in southern Poland, attracting more than one million visitors per year.

With files from The Associated Press