Hundreds of graves found at an Austrian state hospital will be exhumed once the ground thaws to see if any are victims of a Nazi-era purge of patients deemed unworthy to live, authorities said on Tuesday.

The discovery of about 220 bodies in a hospital cemetery during a construction project in Hall, near the Tyrolean capital Innsbruck, aroused suspicions that some of those buried there between 1942 and 1945 were victims of a euthanasia campaign.

"But one should not speak of 220 murder victims," historian Oliver Seifert told Reuters Television, noting that some of the patients buried there may have died of undernourishment or natural causes.

Officials told a news conference a panel of experts would oversee the two-year project to identify the dead from hospital records and genetic samples.

Nazi Germany, which annexed Austria in 1938, introduced mass killings of the physically and mentally handicapped in an effort to eradicate people deemed inferior.

Thousands in Austria died in gas chambers at the Hartheim Castle euthanasia centre near Linz.

At least 360 patients from the hospital in Hall were sent to their deaths before the so-called T4 euthanasia programme officially ended in August 1941, ushering in a new phase in which victims died from neglect, hunger or drug overdoses.

"This phase of 'wild euthanasia' between 1942 and 1945 has really been examined in just a cursory way," Seifert said.

"This is certainly a first step and a good opportunity to see what happened here and how to view it. We know that active killing went on at other institutions in Austria ... but there
are no indications of this at the moment in Hall."

The hospital cemetery in Hall might have been opened in 1942 as part of plans -- never realised -- to set up its own euthanasia station, deputy medical director Christian Haring
said.

"This dark chapter of history must now be carefully examined and cleared up," provincial Governor Guenther Platter told the Austria Press Agency, saying he was deeply shaken by the discovery.