The man who found popular Australian Instagram model Sinead McNamara on the luxury superyacht has revealed how he desperately tried to save her life.

The captain of a neighbouring boat made the horror discovery on the palatial Mayan Queen IV, where McNamara was working off the Greek island of Kefalonia.

According to a friend of the captain, the skipper was returning to his boat about 1.45am on Friday after a night in one of the many bars that surround Argostoli harbour when he saw the young woman.

Port authorities grounded the Mayan Queen IV and its crew to take witness statements and conduct forensic tests. Photo / Supplied
Port authorities grounded the Mayan Queen IV and its crew to take witness statements and conduct forensic tests. Photo / Supplied

The friend said the captain shouted "What are you doing?" and when she didn't answer, he began frantically calling for help.

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Port police officers and the Mayan Queen's own security were then alerted.

The captain has made a statement to the Argostoli Port Authority, which is investigating McNamara's sudden death.

There is no suggestion of foul play and while authorities have not confirmed her cause of death it is believed the young woman took her own life.

The captian said tragically a routine police patrol had just passed the superyacht and not seen the young woman in peril.

The captain described a frantic scramble by police and medics to save McNamara until, after about 30 minutes, they made the decision to fly her to a hospital in Athens.

"We were actually celebrating at first because we thought she had been saved. It was later we heard she had died," the friend told news.com.au.

The 20-year-old from Port Macquarie in NSW died in hospital after hours in a coma.

The captain who witnessed the incident said he was deeply traumatised by the shock encounter.

The superyacht, owned by billionaire Mexican businessman Alberto Bailleres, has now left the Greek island. Mr Bailleres and his family had left two days before McNamara was found on the yacht, with only crew members on board during the incident.

Investigators have footage taken on the yacht's security cameras, suggesting they captured her final moments.

They also are understood to be examining her mobile phone for any messages she may have sent or received last Thursday night.

The captain of a neighbouring boat reportedly saw Sinead McNamara about 1.45am. Photo / via Instagram
The captain of a neighbouring boat reportedly saw Sinead McNamara about 1.45am. Photo / via Instagram

McNamara's death came on what was said to be her final day as a crew member on the Mayan Queen. The model, who had more than 14,000 Instagram followers, had been working on the boat for four months and was soon to be reunited with her sister Lauren and mum Kylie, who were on their way to meet her in Greece.

She posted excitedly about the visit only a week ago. "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," she wrote.

It followed a much darker message on her Instagram profile, in which she wrote: "My head is all over the shop today." The post was accompanied by emojis of a volcano, a tornado and a blood-soaked needle.

She then shared a picture of herself sitting carefree on a quad bike with a caption that said: "Take me back to this where my only worry was not cracking my skull open."

McNamara was active on social media and loved adventure — no more so than in the final weeks of her life.

Her last post detailed how she had been jet skiing in Komitata, Greece.

Greek authorities have said they are investigating the circumstances of McNamara's death and ordered an autopsy. A Port Authority official told news.com.au last night the autopsy results were not yet available.

The 20-year-old has more than 14,000 followers on Instagram. Photo / via Instagram
The 20-year-old has more than 14,000 followers on Instagram. Photo / via Instagram

The Mayan Queen had initially been forbidden from leaving the port, however it left with the blessing of police on Sunday. All 23 crew members had been interviewed prior to the departure.

One local, who had seen the crew members, said they were quiet and visibly upset before they left. Another spoke of seeing several of them "in tears, they were all crying".

WHERE TO GET HELP:

If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111.

OR IF YOU NEED TO TALK TO SOMEONE ELSE:

LIFELINE: 0800 543 354 (available 24/7)
• SUICIDE CRISIS HELPLINE: 0508 828 865 (0508 TAUTOKO) (available 24/7)
YOUTHLINE: 0800 376 633
• NEED TO TALK? Free call or text 1737 (available 24/7)
KIDSLINE: 0800 543 754 (available 24/7)
WHATSUP: 0800 942 8787 (1pm to 11pm)
• DEPRESSION HELPLINE: 0800 111 757​