The Germany-based cruise ship company TUI reports Tuesday that 12 crew members aboard one of its ships touring the Greek islands, who had initially tested positive for COVID-19, showed negative results when they were re-tested.

The company's Mein Shiff 6 cruise ship had departed Sunday from Heraklion in Crete with all 922 passengers having tested negative before boarding. It was the first cruise ship to sail the Greek islands since the COVID-19 lockdown in March.

The company says the ship was cruising off the island of Milos when they were made aware of initial tests results, conducted prior to the cruise.

The results, from tests made of 150 members of the ship's total 666 crew members, detected 12 COVID-19 infections. TUI says the ship headed to Piraeus, Greece's largest port, with better access to health services and equipped to deal with any emergency.

In a statement posted from its Twitter account, the company says once the ship docked, the 12 crewmembers were tested twice - once using the cruise line's Polymerase Chain Reaction (PCR) tests and another by Greek authorities, using rapid antigen tests. They said both showed negative results.

The company statement said the health authorities performed another PCR test, which "should confirm this again." The results of those tests are expected later Tuesday.

TUI went on to say "None of the 12 crew members has any symptoms. The 12 crew members as well as 24 crew members of contact group 1 were immediately isolated on board on Monday."

Those 24 crew members were also subjected to an antigen test by Greek authorities and all results were negative. Until the final results of the PCR tests are available, they will remain isolated, it added.

TUI said that given that no passengers were among the contact group, no tests on them were necessary and the vessel would resume its cruise once Greek authorities give their approval.

The cruise industry has taken a major hit from the pandemic, with some of the earliest large clusters of COVID-19 occurring aboard cruise ships. Voyages of large cruise ships only resumed in recent weeks in Greece after they were banned for months.