Twelve crew members initially tested positive for coronavirus and were placed in isolation on the vessel, which is sailing off Greece. However, all have now been retested and cleared.

Wybcke Meier, Tui Cruises chief executive, said: “Following a false alarm caused by a report of 12 positive test results on crew by a land-based laboratory; three further tests, including two PCR tests and one antigen test, have confirmed the results.

“There are no cases of Covid-19 on board Mein Schiff 6. This was confirmed by the Greek authorities this afternoon.

“The safety of the guests, the crew, but also the Greek population is the top priority for Tui Cruises.

“I would like to thank all the responsible authorities for their good and professional cooperation in connection with the unclear test results on board Mein Schiff 6 and I am pleased that the voyage can be continued for all guests tomorrow with shore excursions in Piraeus.”