Comedic actress Betty White, who starred in globally popular sitcom The Golden Girls, has died just three weeks away from her 100th birthday.

People magazine reported her death today, quoting her agent and close friend Jeff Witjas.

He told the magazine: "Even though Betty was about to be 100, I thought she would live forever."

White capped a career of more than 80 years by becoming America's geriatric sweetheart after Emmy-winning roles on television sitcoms The Golden Girls and The Mary Tyler Moore Show.

In a youth-driven entertainment industry where an actress over 40 is facing 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 likability, White was still starring in a TV sitcom, Hot in Cleveland, at age 92 until it was cancelled in late 2014.

President Joe Biden also tweeted about White's death, describing her as a "cultural icon."

"Betty White brought a smile to the lips of generations of Americans," he tweeted.

She 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.

She played Rose Nylund, a sweet, naive and ditzy Midwesterner, on The Golden Girls, a sitcom about four older women living together in Miami.

Her co-stars included Bea Arthur, playing Dorothy Zbornak, who died in 2009 aged 86. Rue McClanahan, who took the role of Blanche Devereaux, died in 2010 aged 76.

The show ran from 1985 to 1992 and was one of the top-rated series of its time.

Betty White (right) with Golden Girls co-stars Bea Arthur (left) and Rue McClanahan

"Old age hasn't diminished her," the New York Times wrote in 2013. "It has given her a second wind."

Betty Marion White was born on 17 January 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.

Through the 1960s and early '70s she was seen regularly on television, appearing on game shows such as Match Game and Password. She married Password host Allen Ludden, her third and final husband, in 1963.

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 before securing her role on The Golden Girls.

By 2009 she was becoming ubiquitous with more frequent television appearances and a role in the Sandra Bullock film The Proposal.

White's witty and brassy demeanor came in handy as host of Betty White's Off Their Rockers, a hidden-camera show in which older 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."

The actress, who had no children, worked for animal causes. She once turned down a role in the movie As Good as It Gets because of a scene in which a dog was thrown in a rubbish chute.