The 73-year-old actress had been battling with breast cancer for three decades, having previously beaten the illness twice.
Her husband John Easterling took to Facebook this morning to announce the heartbreaking news and now friends and family of the star have started sharing heartfelt tributes to their social media accounts.
Newton-John's daughter, Chloe Lattanzi, took to her official Instagram account to share a series of photos with her mother in the wake of her death.
Three days ago she also shared a heartfelt photo with her mum, calling the Aussie star her "best friend".
Lattanzi said her mother was her 'best friend'. Photo / Instagram @chloelattanziofficial
While her Grease co-star John Travolta issued a touching tribute on his Instagram account, "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 moment I saw you and forever! Your Danny, your John!"
Since I was ten years old, I have loved and looked up to Olivia Newton John. And, I always will. (Just like this picture @nfsaonline) She was, and always will be, an inspiration to me in so many, many ways. My deepest condolences to her family and loved ones. x ONJ4EVER pic.twitter.com/3nE8PVDFLy
Sir Rod Stewart tweeted a goodbye to his "great friend" who he said "was the perfect Lady, gorgeous, with great poise and with a certain Aussie sophistication."
My great friend Olivia Newton John has passed away. She was the perfect Lady, gorgeous, with great poise and with a certain Aussie sophistication. Her spandex trousers in Grease were my inspiration for my ‘Da ya think I’m Sexy‘ era. RIP Olivia Sir Rod pic.twitter.com/Suleq8JSkX
Internationally renowned cook, author, and TV personality Nigella Lawson took to Twitter with a simple but sweet tribute where she called Newton-John's memory a "blessing".
Meanwhile the outspoken talk show host Piers Morgan issued his own heartfelt tribute on his Twitter account, "So sad to hear the fabulously gutsy, warm & talented Olivia Newton-John has died."
Adding, "At an auction of her Grease memorabilia in LA three years ago, she told me her favourite song from the movie was Hopelessly Devoted To You. Great song, great film, great lady. RIP."
So sad to hear the fabulously gutsy, warm & talented Olivia Newton-John has died. At an auction of her Grease memorabilia in LA three years ago, she told me her favourite song from the movie was Hopelessly Devoted To You. Great song, great film, great lady. RIP. pic.twitter.com/K6uteubpPA
Australian-American musician Rick Springfield tweeted a heartfelt message to his long-time friend, saying, "the world is out of balance when we lose these magnificent people."
Sweet Olivia has gone home. She was a beautiful soul and I know of no one who didn’t love her or know what a great humanitarian she was. The world is out of balance when we lose these magnificent people. God speed Livvy. We will all meet again ❤️❤️❤️ @olivianj 💔💔💔 pic.twitter.com/8tV5j8XvII
The Academy paid tribute to the beloved actress by posting a photo of Newton-John and Travolta at the 1978 Academy Awards.
They wrote, "Olivia Newton-John and John Travolta at the 50th Academy Awards (April 3, 1978).
"A few months later, they took the world by storm as Sandy and Danny in 'Grease' - which went on to become the highest grossing film of 1978, proving that Grease is (and forever will be) the word."
Olivia Newton-John and John Travolta at the 50th Academy Awards (April 3, 1978).
A few months later, they took the world by storm as Sandy and Danny in 'Grease' - which went on to become the highest grossing film of 1978, proving that Grease is (and forever will be) the word. pic.twitter.com/MmGrhzDWfC
Award winning actress Viola Davis took to Twitter to express her gratitude for the iconic actress, "Oh man!!! You were my childhood!! Your talent, poise, beauty!! Rest in glorious peace. God bless your family....and thank you for creating eternal memories. "
Oh man!!! You were my childhood!! Your talent, poise, beauty!! Rest in glorious peace. God bless your family....and thank you for creating eternal memories. ❤️❤️❤️❤️ https://t.co/eaS2wmURIh
We have lost a great, iconic artist in Olivia Newton John, gone too soon from us at age 73. I trust she is now in the great Xanadu beyond. Know that we are forever hopelessly devoted to you, Olivia. Rest in song and mirth.
Meanwhile, Australia's Nine Network US correspondent, Alison Piotrowski has reported that fans are gathering at Newton-John's star on the Hollywood Walk of Fame.
Fans coming down to the Hollywood Walk of Fame to pay respects to Olivia Newton-John. RIP Sandy 💔 pic.twitter.com/SBx9g8nwjQ
From 1973-83, Newton-John was among the world's most popular entertainers.
She had 14 top 10 singles just in the US, won four Grammys, starred with Travolta in Grease and with Gene Kelly in Xanadu. The fast-stepping Travolta-Newton-John duet, You're the One That I Want, was one of the era's biggest songs and has sold more than 15 million copies.
