Francis had been hospitalised earlier in July with severe pelvic pain, spending some time in intensive care, manager Ron Roberts said. He did not give the place or cause of death.
With a powerful, clear voice that could be both peppy and plaintive, Francis sold tens of millions of records in the late 1950s and early 1960s, including the skittering lovesick hit "Stupid Cupid" and the lush, maudlin songs "Who's Sorry Now" and "Where the Boys Are."
In 1960, when she was 21, she became the first woman to hold the No 1 spot on the Billboard Hot 100 chart with the release of "Everybody's Somebody's Fool." She went on to record the song in German – "Die Liebe ist ein seltsames Spiel" – and became a keen polyglot in the studio, releasing covers of her hits in Italian, Spanish and several other languages.
Francis was born on December 12, 1937, in Newark, New Jersey, to Italian-American parents who named her Concetta Franconero. A talent scout in the 1950s urged her to change her stage name to something radio DJs might find simpler to pronounce.
In her memoir, she describes her father, who scraped a living as a labourer in the shipyards and factories of New York, as the most powerful force throughout her life, helping her learn to play the accordion as a child.
"I played the accordion the way I did everything else in life – with a vengeance!" she wrote. "Music became my sole focus in life."
It was at his urging, Francis wrote, that she recorded what would become her first hit: "Who's Sorry Now" It was at her father's insistence that she stopped dating the singer Bobby Darin in the 1950s. She described not eloping with Darin as one of her life's greatest regrets.
Earlier this year, her 1962 recording "Pretty Little Baby" became a viral sensation on the social media app TikTok, with users lip-syncing to it in videos seen by millions.
She told People magazine she had forgotten she ever recorded the song.
"To think that a song I recorded 63 years ago is touching the hearts of millions of people is truly awesome," she said.
