Former Nazi SS guard Oskar Groening, dubbed the "bookkeeper of Auschwitz", has asked for "forgiveness" at the start of his trial on 300,000 counts of accessory to murder.

"For me there's no question that I share moral guilt," the 93-year-old German told the judges, admitting that he knew about the gassing of Jews and other prisoners.

"I ask for forgiveness," he said at the trial, which was attended by almost 70 Holocaust survivors and victims' relatives, while insisting he never physically harmed a prisoner himself.

"You have to decide on my legal culpability."

Given the advanced age of most Nazi war crimes suspects, Groening is expected to be among the last to face justice, 70 years after the liberation of the concentration camps at the end of World War II.

He is facing trial in the northern city of Lueneburg on 300,000 counts of accessory to murder in the cases of deported Hungarian Jews who were sent to the gas chambers in 1944.

He faces up to 15 years in jail.

Prosecutors said Groening served as a bookkeeper who sorted and counted the money taken from those killed, collecting cash in different currencies from across Europe.

He also performed "ramp duty", guarding the luggage stolen from deportees as they arrived by rail at the extermination and forced labour camp in Nazi-occupied Poland, they said.

Prosecutor Jens Lehmann said the defendant, by diligently performing his daily duties, had made "at least a low-level contribution" to the "smooth operation" of the death camp.

Asked to be sent to front after seeing baby killed

Groening, a widowed father of two adult sons, entered court using a walking frame.

He said that as a young man he had volunteered for the SS because, in the fervour of wartime, "we wanted to be part of it", insisting he knew nothing at the time about the gas chambers.

Speaking in a firm voice, he recounted acts of barbarism he witnessed at Auschwitz, including when an SS guard killed a crying baby by smashing its head against a truck.

Groening said he was "shocked" and asked to be transferred to the front three times, but that his requests were denied.

An estimated 1.1 million people were killed at the Auschwitz-Birkenau concentration camp during World War II. ( File photo: Reuters )

The defendant also said that he once passed a gas chamber and heard cries "growing louder and more desperate, until they fell silent".

Reflecting on the Holocaust, he said: "What kind of hatred was behind it? I just can't understand it."

The more than 100 co-plaintiffs, witnesses, lawyers and reporters listened to him in German or via simultaneous translations in English, Hebrew and Hungarian, in the court, a converted auditorium.

Romanian-born Auschwitz survivor Eva Kor, 81, said before the trial that "he is a murderer because he was part of the system of mass murder".

But after Groening's testimony, she expressed appreciation for his attempt to shine a light on his dark past.

"He's very old, and meeting him face-to-face makes me realise that he did the best that he can do with his mind and his body, because he has a lot of difficulties physically and, I'm sure, emotionally," she said outside the court.

"He has to remember a lot of things he did, so I think he is really doing his best."

Groening had been open about his past as a Nazi

Groening, unlike most former Nazis, has often spoken in media interviews about what he did and saw at Auschwitz.

He first opened up about his past in 1985, when a member of his stamp collectors' club handed him a book written by a Holocaust denier.

Groening returned it with the message "I saw everything. The gas chambers, the cremations, the selection process... I was there."

He went on to write a memoir for his family, shared his recollections with the German press and appeared in a BBC documentary.

Groening had previously been cleared by German courts, but the legal basis for prosecuting ex-Nazis changed in 2011 with the trial of former death camp guard John Demjanjuk.

While previously courts had punished defendants for individual atrocities, Demjanjuk was convicted solely on the basis of having served at the Sobibor camp in occupied Poland.

Some 1.1 million people, most of them European Jews, perished between 1940 and 1945 in the Auschwitz-Birkenau camp before it was liberated by Soviet forces.

The trial, which adjourned later Tuesday, is scheduled to run until July 29.

AFP