Poland has reopened investigations into crimes committed at the Nazi death camp of Auschwitz during World War Two, in an effort to track down any surviving camp employees before they die.

Up to 1.5 million people, mostly Jews, perished at Nazi German hands at Auschwitz, near the city of Krakow in southern Poland, during the war that ended in 1945.

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In the postwar communist era, Warsaw launched probes into crimes committed at Auschwitz, but closed them in the 1980s because questioning witnesses and perpetrators based abroad was too hard at a time when Poland was part of the Soviet bloc.

"We do not exclude the possibility of finding alive former employees of the Auschwitz-Birkenau concentration camp," Piotr Piatek of Poland's Institute of National Remembrance (IPN) told the PAP state news agency on Thursday.

"In this case they may be accused of crimes against the Polish nation," he said.

The IPN is a state institution that investigates communist-era and Nazi-era crimes and can prosecute those it considers to have committed "crimes against the nation".

It was not immediately clear whether the reopened investigation would cover other Nazi death camps that operated on Polish soil during the war.

Jewish groups welcomed Thursday's announcement by the IPN.

"(We) welcome this effort to belatedly bring to justice and public awareness the perpetrators of the monstrous crimes the Nazis inflicted on the world's conscience more than half a century ago," said Elan Steinberg of the American Gathering of Holocaust Survivors and their Descendants.

"It is not only justice that is being served, but the purposeful values of education and remembrance that will give meaning to this undertaking."