Greek authorities now believe an Australian Instagram model whose unconscious body was found tangled in rope on a superyacht may have taken her own life.

Sinead McNamara, 20, from Port Macquarie in northern New South Wales, had been working as a crew member on the Mayan Queen IV for four months.

The luxury yacht is owned by Mexican businessman Alberto Bailleres, who chairs Mexico's second-largest mining company and is worth $9.6billion.

'By the looks of it, she took her life,' a senior officer told The Sunday Times. 'We expect the autopsy to verify this in the coming days.'

Just two weeks before her death, the young model penned a cryptic Instagram post which takes on a tragic new meaning in light of her sudden passing.

'My head is all over the shop today. Take me back to this where my only worry was not cracking my skull open,' she wrote alongside a photo of herself on a quad bike.

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Instagram star Sinead McNamara, 20, from Port Macquarie on the NSW mid-north coast, was found unconscious on a superyacht

An autopsy has been ordered by Greek authorities to identify the cause of death for the young Australian (pictured)

Ms McNamara was found on the back of the boat (pictured) on Thursday. She died while being airlifted to hospital in Athens

Sinead penned a cryptic Instagram post (pictured) two weeks before her death

Kefalonia Police told The Australian the Argostoli Port Authority was investigating her death with port officials expected to provide a further update later on Monday.

Investigators are waiting for the autopsy results to determine the cause of death.

Greek media have reported that while Ms McNamara's death may appear to be non-suspicious, police still want to rule out foul play.

The luxury yacht was due to depart Kefalonia on Sunday but has been ordered to remain at the port for ongoing investigations.

Detectives will interview all the crew members, understood to be no more than 24 people, before completing a thorough forensic examination of the superyacht.

Members of the crew have been ordered to remain on board until the investigation is complete.

Investigators are still waiting for the autopsy results so they can confirm what happened to Sinead (pictured)

The luxury yacht is owned by ultra-rich Mexican businessman Alberto Bailleres (pictured) who is worth an estimated $9.6billion

Sinead (pictured) died while being airlifted by helicopter to an Athens hospital

Local media reports indicate Mr Bailleres left the boat on Tuesday, when it was anchored at the Greek island of Kefalonia.

The billionaire business tycoon had been holidaying on the boat before he and his family planned to return to Mexico.

Ms McNamara's body was found on the back of the boat late on Thursday night and she was transferred to a local hospital, local media reported.

Despite desperate attempts from crew members, emergency services and port officials, she fell into a coma.

She died while being airlifted by helicopter to an Athens hospital.

Ms McNamara's mother, Kylie, and sister were in the air flying to Greece to visit the influencer when they were told the news of her death.

Greek authorities are trying to piece together the mysterious death of the much-loved model

Jake McNamara (pictured, right), the brother of the social media influencer, confirmed her death on Saturday

Few details on the death of the 20-year-old have been released, but the family believes Ms McNamara died in a boating accident, The Daily Telegraph reported.

The Department of Foreign Affairs and Trade said it has offered support to the McNamara family.

'The Department of Foreign Affairs and Trade is providing consular assistance to the family of an Australian who died in Greece,' a spokeswoman said.

Jake McNamara, the brother of the social media influencer, confirmed her death on Saturday.

'I have unfortunately received the worst news of my life, (Sinead) has passed away,' her brother Jake McNamara said (pictured is Ms McNamara)

'I have unfortunately received the worst news of my life, (Sinead) has passed away,' Mr McNamara said.

Ms McNamara was travelling in the seaside town of Pylos on the southwest coast of Greece.

The 20-year-old was active on social media and loved adventure, travel and camping.

Her final post has been inundated with love from her followers offering their condolences to her family and friends.

Just four days ago, Ms McNamara said she was 'jet skiing around the most beautiful turquoise water in the med,' referring to the Mediterranean Sea.

Ms McNamara posted on Facebook on Monday that she was excited to see 'the most amazing big sister I could ever ask for' (pictured)

The 20-year-old had been working as a crew member on the Mayan Queen IV for four months

Ms McNamara posted on Facebook on Monday that she was excited to see 'the most amazing big sister I could ever ask for.'

Loved ones posted to Ms McNamara's Facebook and Instagram accounts, sharing fond memories with the young Instagram model.

One friend said, 'It was only a few days ago you were messaging me forcing me to come camping with you. You're such a gorgeous girl lost way to soon.'

Another said 'You lived more in your short years than most do in a lifetime, thanks for all the memories. Rest easy x'

One friend said, 'It was only a few days ago you were messaging me forcing me to come camping with you. You're such a gorgeous girl lost way to soon.' (pictured is Ms McNamara)

'Our souls were so perfectly aligned we were convinced we were the same person. I can't explain how much I'm going to miss you or how broken I am.'

Australian YouTuber Alex Hayes posted the heartbreaking news to his social media accounts.

The social media star who has more than 650,000 followers on Instagram posted the news to his Instagram story.

'Life is so precious gone was too soon. Such a beautiful human being. Will cherish all our memories. Rest in Peace you beautiful soul.

Australian YouTube star Alex Hayes (right) posted the heartbreaking news to his social media accounts