Her agent, Jeff Witjas, told People magazine on Friday: "Even though Betty was about to be 100, I thought she would live forever."
No cause was cited.
In a youth-driven entertainment industry where an actress over 40 faces career twilight, White was an elderly anomaly who was a star in her 60s and a pop culture phenomenon in her 80s and 90s.
Playing on her imminent likeability, White was still starring in a TV sitcom, Hot In Cleveland, at age 92 until it was cancelled in late 2014.
White said her longevity was a result of good health, good fortune and loving her work.
"It's incredible that I'm still in this business and that you are still putting up with me," White said in an appearance at the 2018 Emmy Awards ceremony, where she was honoured for her long career.
"It's incredible that you can stay in a career this long and still have people put up with you. I wish they did that at home."
White was not afraid to mock herself and throw out a joke about her sex life or a snarky crack that one would not expect from a sweet-smiling, white-haired elderly woman. She was frequently asked if, after such a long career, there was anything she still wanted to do and the standard response was: "Robert Redford."
"Old age hasn't diminished her," the New York Times wrote in 2013.
"It has given her a second wind."
Minutes after news emerged of her death, US President Joe Biden told reporters: "That's a shame. She was a lovely lady."
His wife Jill Biden said: "Who didn't love Bette White? We're so sad about her death.'
Betty Marion White was born on January 17, 1922, in Oak Park, Illinois, and her family moved to Los Angeles during the Great Depression, where she attended Beverly Hills High School.
White started her entertainment career in radio in the late 1930s and by 1939 had made her TV debut singing on an experimental channel in Los Angeles. After serving in the American Women's Voluntary Service, which helped the US effort during World War II, she was a regular on Hollywood On Television, a daily five-hour live variety show, in 1949.
A few years later she became a pioneering woman in television by co-founding a production company and serving as a co-creator, producer and star of the 1950s sitcom Life With Elizabeth.
White reached a new level of success on The Mary Tyler Moore Show, playing the host of a home-making television show, the snide, lusty Sue Ann Nivens, whose credo was "a woman who does a good job in the kitchen is sure to reap her rewards in other parts of the house." White won best-supporting actress Emmys for the role in 1975 and 1976.
She won another Emmy in 1986 for The Golden Girls, a sitcom about four older women living together in Miami that featured an age demographic rarely highlighted on American television.
By 2009 she was becoming ubiquitous with more frequent television appearances and a role in the Sandra Bullock film The Proposal. She starred in a popular Snickers commercial that aired during the Super Bowl, taking a brutal hit in a mud puddle in a football game.
White's witty and brassy demeanour came in handy as host of Betty White's Off Their Rockers, a hidden-camera show in which elderly actors pulled pranks on younger people.
"Who would ever dream that I would not only be this healthy, but still be invited to work?" White said in a 2015 interview with Oprah Winfrey.
"That's the privilege ... to still have jobs to do is such a privilege."
