Olivia Newton-John has been hailed as an "angelic voice" who produced "stone cold classic" songs following her death aged 73.
The British-born singer died "peacefully" at her ranch in southern California on Monday morning, surrounded by family and friends, her widower confirmed.
Leading the tributes from the entertainment world was John Travolta, who starred opposite Newton-John in the hit 1978 film Grease.
Writing on Instagram, Travolta said her "impact was incredible" and signed off his tribute as "your Danny":
"My dearest Olivia, you made all of our lives so much better.
"Your impact was incredible. I love you so much. We will see you down the road and we will all be together again.
"Yours from the first moment I saw you and forever! Your Danny, your John!"
Her performance in Grease saw her nominated for multiple awards including two Golden Globes, and various other film accolades.
She is also a multi-platinum selling singer, with two singles and two albums having earned the stamp from the Recording Industry Association of America.
Newton-John also represented the UK in the 1974 Eurovision Song Contest with the song Long Live Love. She finished fourth in the competition, held in Brighton, losing out to Abba, with their hit song Waterloo.
In a statement posted to Instagram, her husband John Easterling wrote:
"We ask that everyone please respect the family's privacy during this very difficult time.
"Olivia has been a symbol of triumphs and hope for over 30 years sharing her journey with breast cancer.
"Her healing inspiration and pioneering experience with plant medicine continues with the Olivia Newton-John Foundation Fund, dedicated to researching plant medicine and cancer."
Mr Easterling added that in lieu of flowers, donations be made to Dame Olivia's foundation.
She is survived by her husband as well as her daughter Chloe Lattanzi.
Olivia Newton-John's life included drama and heartache, but she'll be remembered for her "girl-next-door" appeal and her sweet singing voice.
Newton-John battled and defeated breast cancer in 1992 before its reappearance in 2013, and the British-born Australian has died at her ranch in Southern California on Monday aged 73.
Newton-John was born on September 26, 1948, in Cambridge, England, where her father Bryn had been working on the Enigma project at Bletchley Park during WWII.
When she was six years old her family emigrated to Melbourne, where she attended Christ Church Grammar School and University High School.
After winning a trip to the UK on a TV talent show, Newton-John decided to try her luck in Great Britain where she recorded and released her first single for Decca in 1966.
International success eluded her until her first solo album in 1971, when the singles If Not For You and Banks of the Ohio charted around the world.
That began a string of hits including Let Me Be There, her signature tune I Honestly Love You, and 1981's Physical which topped the US charts for 10 consecutive weeks.
During her life Newton-John received four Grammy Awards, an Emmy Award, numerous Country Music Awards, American Music Awards and People's Choice Awards.
Her acting career took off in 1978, when the world fell in love with her as the sweet Sandy Olsson in the movie musical Grease alongside John Travolta, and two years later she danced with screen legend Gene Kelly in Xanadu.
The singer kept her head high through the mysterious disappearance of her boyfriend of nine years, Patrick McDermott, who was thought to have drowned off the coast of California in 2005 until evidence emerged in 2009 suggesting he had faked his death and was hiding in Mexico.
Despite the tough breaks in her personal life, Newton-John always bounced back, turning tragedy into a positive force with charities and movements ranging from cancer research to the environment.
In 1991, Newton-John turned tragedy into a cause that would help others when her daughter, Chloe, lost her best friend, Colette Chuda, to cancer. Newton-John helped form the Colette Chuda Environmental Fund in the United States, assisted with the foundation of Australia's Planet Ark organisation in 1993 and served as Goodwill Ambassador to the United Nations Environment Programme.
She also actively supported Melbourne's Austin Hospital in building the Olivia Newton-John Cancer Wellness and Research Centre, and promoted the LIV-KIT device for breast cancer detection.
Newton-John received many honours including being appointed an Officer in the Order of Australia (OA) in 2006. That followed an Order of the British Empire (OBE) honour bestowed upon her by Queen Elizabeth II in 1979. In 2012 the National Trust of Australia named her a National Living Treasure.
One of Newton-John's latest awards came in 2006 at the G'day LA Ball in Hollywood, where she was presented with a Lifetime Achievement Award by Travolta. Travolta said he admired how Newton-John had survived the ups and downs in her life:
"We've been friends for 28 or 29 years and we have always been there for each other no matter what, thick or thin."
In May 2017 the singer announced she was cancelling a tour due to the recurrence of her breast cancer, which had metastasised to her back and would be undergoing treatment at the cancer centre named after herself in Melbourne.
Newton-John married twice, first in 1984 to actor Matt Latanzi after they met on the set of Xanadu.
The couple divorced in 1995 and in 2008 Newton-John secretly wed John Easterling, the founder of natural remedy firm Amazon Herb Company.
Australian pop icon Kylie Minogue tweeted:
Dionne Warwick, who recorded a duet with Newton-John in 2006, tweeted:
"Another angelic voice has been added to the Heavenly Choir.
"Not only was Olivia a dear friend, but one of the nicest people I had the pleasure of recording and performing with. I will most definitely miss her.
"She now Rests in the Arms of the Heavenly Father."
Oscar-winning actress Marlee Matlin tweeted her memory of starring alongside Newton-John in the 1996 film It's My Party, one of the first films to address the topic of Aids patients dying with dignity:
"I am SO saddened at the news of the passing of Olivia Newton John.
"I remember being so star struck when I met her at my first Hollywood gathering for Paramount.
"She was the sweetest and brightest light and I loved getting to know her on It's My Party. RIP dear, sweet Olivia."
American filmmaker and actor James Gunn tweeted about his "first real crush" and revealed he previously bought her home in Malibu:
"Really sad to hear about the passing of Olivia Newton-John.
"My first real crush as a kid.
"I loved Grease & her music & I coincidentally also bought & lived in for a while the wonderful home she built in Malibu. May she Rest In Peace."
Filmmaker Edgar Wright, whose credits include Last Night in Soho and Baby Driver, added:
"Olivia Newton John so completely dominated the charts and Top Of The Pops when I was a kid, it felt like she was pop music.
"And yes, Xanadu is still a stone cold classic song. RIP."
Kiss co-founder and frontman Paul Stanley said in a brief tribute: "So very sad. She was everyone's sweetheart."
Actress Gabrielle Union described the impact on her of Newton-John's performance in Grease.
"Grease is my #1 movie of all time and made me a lifelong Olivia Newton John fan.
"Me and my sister watched Xanadu more times than I could count.
"Sending so much love and prayers to a real gift of a woman and talent."