She later posted a photo of herself and Newton John smiling and embracing with the caption: "Just giving you the heads up that Livvy is in good health, so let's leave that distressing rumour where it belongs."
The iconic actress and singer is battling breast cancer and a tumour on the base of her spine, but American gossip site Radar Online claims her body is "shutting down".
Some Australian media outlets seized on the unconfirmed reports, sparking a frenzy of activity on social media from her worried fans.
It's believed this cover of the National Enquirer tabloid in the US sparked the rumours. Photo / Supplied
The local website Now To Love claims that people close to Newton-John, 70, say she is struggling with her cancer battle and her prognosis is "weeks, not months".
But those in the star's inner-circle have told news.com.au that ONJ is A-OK.
An Australian source said Newton-John, famed for her role in Grease and a string of musical hits, is perfectly well and had enjoyed the Christmas and New Year period.
Her American representative Michael Caprio laughed when contacted by news.com.au, saying reports of his client's imminent demise were "hilarious".
"No she has not," Caprio said. "You might want to get better sources versus reading tabloids."
And her social media manager Randy Slovacek told The Herald Sun newspaper: "We have stated over and over again publicly she's feeling better. People just seem to want to believe some dramatic turn."
It's understood the Radar Online story followed a report in the dubious US tabloid National Enquirer, which touted a "tragic world exclusive" late last month.
"THE END," its headline read. "Losing third fight with cancer; going home to die on her ranch."
Newton-John was first diagnosed with breast cancer in 1992 and managed to beat it. A second occurrence in 2013, that time in her shoulder, was kept a secret from the world.
In 2017, she decided to go public with her third battle and spoke of her mix of treatments — radiation as well as more natural remedies, as well as cannabis oil.
Her initial battle inspired her to open the Olivia Newton-John Cancer Research Institute, which works to find breakthroughs and treatments.
It also operates the Olivia Newton-John Cancer Wellness Centre, which provides world-leading treatment complemented by wellness programs and clinical trials.
The claims about her health swirling today, which again her spokesman has strongly denied, have prompted an outpouring of shock and grief from fans.
Olivia Newton-John has 'weeks' to live, according to new reports == a SUPERSTAR we will miss her badly
