Greek authorities are trying to piece together the mysterious death of an Australian Instagram model whose body was found on a yacht.

Sinead McNamara, 20, from Australia was found in a critical condition on the vessel on Thursday, and died while being airlifted to hospital.

The 92-metre yacht owned by Alberto Baillères, an 87-year-old mining magnate, has been ordered by the Hellenic Coast Guard to remain docked at the port of Argostoli, on the Ionian island of Kefalonia, while detectives interview crew members and forensic tests are carried out.

Billionaire Baillères wasn't on board his ship at the time of the incident, according to local media.

Only days before her death, the model was posting snaps for her 18,000 Instagram followers, including shots of the scenic Greek islands and bikini shots aboard the super yacht.

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Greek authorities are now investigating the circumstances surrounding the 20-year-old's death. "We expect the autopsy to verify this in the coming days".

Her death was announced by her brother Jake McNamara who posted on social media that he has "unfortunately received the worst news of my life, (Sinead) has passed away".

The Department of Foreign Affairs and Trade is providing consular assistance to Ms McNamara's family. Her mother and sister had flying to Greece to meet her when they were informed of her passing. Local media outlets in Greece say McNamara tried to commit suicide aboard the mega ship, citing anonymous sources.

Sinead last posted five days ago from Komitata, Kefalonia in Greece while jet skiing "around the most attractive turquoise water in the med".

Her final post has been inundated with love from her followers offering their condolences to her family and friends. "Rest in Peace you attractive soul", he wrote. Will cherish all our memories.