The 20-year-old McNamara was found unconscious around 2 a.m. Friday on the back of the Mayan Queen IV in the Greek port of Argostoli in Kefalonia, news.com.au reported.

The doctor on the yacht and port authority officials attempted to revive her as a helicopter arrived at the scene to transport her to a hospital.

She died while heading to the hospital, local reports stated. Her cause of death has not been revealed.

“The Coast Guard of Kefalonia has ordered an investigation into the circumstances that led to the death of the 20-year-old Australian national as well as an autopsy-necropsy,” local media In Kefalonia reported.

McNamara, who was described as an Instagram model with more than 15,000 followers, had been working on the $140 million yacht for the last four months.

The 300-foot yacht is owned by Mexican mining magnate Alberto Bailleres, who is worth an estimated $6.9 billion.

Bailleres was reportedly not in Greece when McNamara died. He had left the yacht on Tuesday and McNamara stayed on the vessel with the crew. It’s unclear what occurred in the next few days leading up to her death.

Authorities have ordered the yacht to remain at the port as the investigation continues.

Reports say the model was working on yachts while she traveled through Europe. Her mother, Kylie, was heading to Greece when she was told her daughter died.

McNamara was supposed to travel to the Greek town of Pylos before her death.

“I have unfortunately received the worst news of my life; Sinead has passed away,” her brother Jake McNamara told a news outlet The Australian.

McNamara was also expected to meet up with her sister Lauren. She wrote about her excitement to see her sister days ago in a birthday post.

“Happy birthday to the most amazing big sister I could ever ask for, 5 days till I get to see you!!! Excitement is an understatement,” McNamara wrote on Instagram.

McNamara friends and followers have flooded the model’s social media pages with their condolences, saying they were shocked by her sudden death.