German special prosecutors have recommended that 30 former Auschwitz death camp guards be tried on charges of accessory to murder during World War II.

Kurt Schrimm, head of the federal prosecutors' office in Ludwigsburg, said that an investigation of 49 guards had resulted in 30 of them being referred to state prosecutors for their roles at the biggest Nazi death camp.

The 30 accused live in Germany. A further seven who live outside the country are still being investigated. Those living abroad are in Austria, Brazil, Croatia, the US, Poland and even one in Israel. They are said to be aged between 87 and 97.

The cases are being delivered to the state prosecutors' offices in 11 of Germany's 16 states who . will decide whether the suspects are fit to stand trial.

"The biggest enemy is time," Schrimm told reporters.

The murder charges can be filed under the same legal framework used by Munich prosecutors against Ukrainian-born John Demjanjuk, who served as a guard at Sorbibor and Majdanek. Demjanjuk, who died in a Bavarian nursing home in 2012, was convicted solely on the basis that he was a camp guard. There was no evidence that he was involved in inmates' deaths.

Top Nazi hunter Efraim Zuroff at the Simon Wiesenthal Centre in Jerusalem said the decision to prosecute 30 suspected former guards could pave the way for more cases.

"We commend the [prosecutors]) for seeking to apply the precedent as widely as possible and hope that they will be able to find as many perpetrators as possible," he said.

"It's only a shame that this kind of legal reasoning was not applied previously because it would have led to many more cases of people who deserved to be brought to justice."

The Nazis built six main death camps, all in occupied Poland: Auschwitz, Belzec, Chelmno, Majdanek, Sobibor and Treblinka.

More than 1.3 million people were gassed and murdered at Auschwitz alone. Ninety percent of them were Jewish.

Nine of the 49 suspected Auschwitz guards have died. More than 7,000 SS personnel served at the Auschwitz-Birkenau camp complex in 1940-45, but only a few hundred were ever prosecuted.