ATHENS, Greece — Greek authorities say 12 crew members of a Maltese-flagged cruise ship on a Greek island tour with more than 1,500 people on board have tested positive to the coronavirus and have been isolated on board.

The Mein Schiff 6, operated by TUI Cruises, began its trip in Heraklion on the southern Greek island of Crete on Sunday night, with 922 passengers and 666 crew members on board, Greece's Shipping Ministry said Monday. It had been due to sail to Piraeus, the country's main port near the Greek capital, Athens, and later to the western island of Corfu.

Sample tests for the coronavirus were carried out on 150 of the crewmembers, the ministry said, and 12 of them were found to be positive. The passengers had undergone coronavirus tests before boarding and were not part of the sample testing.

Those who tested positive for COVID-19 had been isolated on board, and the cruise ship was headed to Piraeus.

Greek health authorities said the ship was expected to arrive on Tuesday, and a National Public Health Organization team would be on hand to re-test the 12 positive cases, as well as anyone else deemed necessary by the ship's crew and on-board doctor. The health authority said all 12 of those who had tested positive were asymptomatic and with a "low viral load."