Rainer Schnitzler, the mayor of the town where she lived said the legendary director and photographer died late on Monday at her home in the Bavarian town of Poecking.
"Her heart just stopped beating," Riefenstahl's longtime companion Horst Kettner told the online edition of lifestyle magazine Bunte.
Riefenstahl had just celebrated her 101st birthday on 22 August lying quietly in bed recovering from a cancer operation.
Although widely admired as one of the world's great filmmakers, Riefenstahl remained deeply controversial because her two major works were funded by, and intended to glorify, Hitler's rule.
They were Triumph of the Will in 1934 which all but deified Hitler, and Olympia in 1936, a record of the Olympic Games staged in Berlin that year.
The works were unprecedented in their content and technique, recognised then and now as near-perfect masterpieces, documenting the force and beauty of the human figure.
Born in 1902 into a lower middle-class family in Berlin, Riefenstahl embarked on a career as a dancer over the objections of her family.
Although widely admired as one of the world's great filmmakers, Riefenstahl remained deeply controversial.
An injury made her switch to acting, but it was not long before she took to directing and in 1932 released her first acclaimed film, The Blue Light, in which she also starred.
Among its many admirers was Hitler, who came to power in 1933 and quickly commissioned his ambitious propaganda films.
Riefenstahl was shunned in Germany after World War II despite being cleared of Nazi guilt by the Allies.
After avoiding the public eye for decades, she turned her attention to the Nuba tribesmen in Sudan in the 1970s.
Although the photographs were widely praised for their striking aesthetic richness, critics accused her of dehumanising her subjects and awakening memories of her earlier work.
Riefenstahl took up diving at the age of 71 - telling her instructor she was 20 years younger - and launched a new phase of her career documenting life in the seas of the Indian Ocean, based on about 2000 dives over 25 years.
Although those films were also well received, the temperamental artist often complained in interviews that her work had been reduced to the few years she worked for Hitler.
Asked before her 100th birthday what title she would give any film about her centenary, she said, "Loved, persecuted and unforgotten."