Sixto Rodriguez, the once obscure American singer-songwriter who found a career renaissance after his music developed a cult following abroad, has died at the age of 81, according to his website.

"It is with great sadness that we at Sugarman.org announce that Sixto Diaz Rodriguez has passed away" on Tuesday, the statement read, without providing a cause of death for the singer, whose hits included "Sugar Man" and "I Wonder."

Born July 10, 1942 in Detroit to Mexican-American parents, Rodriguez worked on assembly lines while moonlighting as a musician, putting out two albums in the 1970s: "Cold Fact" and "Coming From Reality."

By most metrics they bombed stateside, and Rodriguez quit the music industry and lived a quiet, working-class life in Detroit.

The musician had no idea that his music, and in particular "Sugar Man," found a massive following throughout apartheid-era South Africa as well as in New Zealand and Australia.

That he was not a public presence fuelled fan beliefs that Rodriguez was dead.

But the internet changed Rodriguez's life: his daughter Eva found websites devoted to her father, and fans tracked him down before he played a successful 1998 South African tour.

"I told him, 'In South Africa, you're bigger than Elvis,'" said one devotee, Stephen Segerman, in an interview with The Detroit News in 2008.

The remarkable story was immortalised in a 2012 documentary "Searching for Sugar Man," which went on to win an Oscar as well as give Rodriguez belated success in the United States and a music career resurgence. (AFP)