The reports are based on a photo shared by their friend Conrad Carr on Instagram stories which appeared to show them cutting a wedding cake. There are 'Mr and Mrs' balloons in the background.
Various family members including Cyrus' mother Trish and Hemsworth's brothers are seen in the pictures.
Cyrus is pictured wearing an ivory wedding-style gown in an off-the-shoulder style. Hemsworth, who has been in an on-off relationship with the singer for around eight years, is seen wearing a tux.
'Incredible' vegan partner
Cyrus spoke out about her love for Hemsworth earlier this month on the Howard Stern radio show, describing him as 'incredible' while talking about the wildfires that raged through California last month.
"He got all the animals out in his truck," she said during the segment. "He put two pigs in crates, which, I can tell you, is so hard....I've never loved him more for this."
Sharing a message about the fires at the time, Cyrus said: "I am one of the lucky ones. My animals and LOVE OF MY LIFE made it out safely and that's all that matters right now."