According to reports from Jürgen's Swiss management company, the entertainer died of heart failure on Sunday during a walk in Gottlieben, in western Switzerland.
Despite immediate attempts at resuscitation, Jürgens died in a nearby hospital in the town of Münsterlingen. He was 80 years old.
The singer spoke to Germany's Bild.de magazine two weeks ago, explaining that he 'felt wonderful', and was looking forward to moving into a new home.
His last performance was on December 7th.
He was a composer and singer of popular music whose career spanned more than fifty years.
Jürgens, who was born in Klagenfurt, wrote more than 800 songs and sold over 100 million records. In 2007 he obtained Swiss citizenship, while retaining his Austrian passport.
He won the Eurovision song contest in 1966 with "Merci cherie" which was a hit in several languages, including French, English, Dutch and Italian.
In his 2004 autobiography "Der Mann mit dem Fagott" ("The man with the bassoon"), Juergens wrote extensively about growing up a "good Hitler youth" as a little boy in Austria and later regretting the ignorance of his youth, according to the New York Times.
"We were all but castrated after the war," he said in a 2004 interview with the Swiss magazine Schweizer Illustrierter. "But Judaism must find a homeland in this country, it must return. That is my greatest dream. I'm attached to this culture with all my heart."