A German court on Tuesday handed a five-year jail sentence to a 101-year-old former Nazi concentration camp guard, the oldest person so far to go on trial for complicity in war crimes during the Holocaust.

Josef Schuetz was found guilty of being an accessory to murder while working as a prison guard at the Sachsenhausen camp in Oranienburg, north of Berlin, between 1942 and 1945, presiding judge Udo Lechtermann said.

The pensioner, who now lives in Brandenburg state, had pleaded innocent, saying he did "absolutely nothing" and was not aware of the gruesome crimes being carried out at the camp.

"I don't know why I am here," he said at the close of his trial on Monday.

But prosecutors said he "knowingly and willingly" participated in the murders of 3,518 prisoners at the camp and called for him to be punished with five years behind bars.

More than 200,000 people, including Jews, Roma, regime opponents and gay people, were detained at the Sachsenhausen camp between 1936 and 1945.

Tens of thousands of inmates died from forced labour, murder, medical experiments, hunger or disease before the camp was liberated by Soviet troops, according to the Sachsenhausen Memorial and Museum.

Prosecutors said Schuetz had aided and abetted the "execution by firing squad of Soviet prisoners of war in 1942" and the murder of prisoners "using the poisonous gas Zyklon B".

He was 21 years old at the time. (AFP)