Three Jewish Auschwitz survivors have testified in the second day of the trial of a former SS sergeant alleged to have served as a guard in the Nazi death camp.

The defendant, 94-year-old Reinhold Hanning, showed no emotion as the witnesses told of crematoria chimneys belching out flames, naked prisoners being taken to the gas chambers and people being shot before their eyes.

Prosecutors argue that Hanning is guilty of 170,000 counts of accessory to murder because he helped the death camp complex function, even though there is no evidence of him committing a specific crime.

About 40 survivors and their families have joined the trial as co-plaintiffs as allowed under German law. The trial is scheduled to hear three more when testimony resumes next Thursday.