A total of 57 sailors have been infected with the coronavirus after 35 days at sea - despite all testing negative for the deadly disease before leaving.
The Echizen Maru fishing trawler returned to port in Argentina after some of the crew began showing symptoms of Covid-19.
According to the health ministry for the southern Tierra del Fuego province, 57 sailors, out of 61 crew members, were diagnosed with the virus after undergoing a new test.
However, all of the crew members had undergone 14 days of mandatory quarantine at a hotel in the city of Ushuaia. Prior to that, they had negative results, the ministry said in a statement.
Of the four remaining sailors, two tested negative and two are still waiting for results. According to reports, two sailors had to be hospitalised.
Alejandra Alfaro, the director of primary health care in Tierra del Fuego said in a statement: "It's hard to establish how this crew was infected, considering that for 35 days, they had no contact with dry land.
"Supplies were only brought in from the port of Ushuaia."
She added that a team is examining 'the chronology of symptoms in the crew to establish the chronology of contagion'.
Alfaro also explained that there is a security cordon around the boat to ensure there is 'nobody getting on or off without permission'.
According to MailOnline, Leandro Ballatore, the head of the infectious diseases department at Ushuaia Regional Hospital, said he believed this is a 'case that escapes all description in publications, because an incubation period this long has not been described anywhere'.
He added: "We cannot yet explain how the symptoms appeared."
The Buenos Aires Times reported that the trawler belongs to a firm called Pesantar, which is part of the New San group - one of the main manufacturers of electronic products in the province.
Argentina exceeded 100,000 coronavirus cases on Sunday (12 July) and they have had 1,859 deaths to date. The majority have been in the Buenos Aires Metropolitan Area.
The publication stated that domestic tourism re-opened in Tierra del Fuego in late June after more than a month of no new cases.
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