The first cruise to return to service since the beginning of the pandemic came to an abrupt end as dozen crew members tested positive for the coronavirus, the German operator TUI confirmed Monday.

"Early on Monday we received positive test results for 12 crew members from an external laboratory," the Hamburg-based operator said.

The Maltese-flagged Mein Schiff 6 had set sail with nearly 1,000 passengers from Heraklion on Crete Sunday night, local media reported.

According to media reports, out of the 666 member crew, 12 have tested positive for the coronavirus. After the results came in, the captain interrupted the cruise and halted it near the small island Milos, awaiting instructions.

"They have been isolated on board, and we are awaiting instructions from the public health agency on where the ship is to sail," said coastguard spokeswoman, adding that the passengers had a clean bill of health before the trip.

It was now expected to sail to Piraeus. The infected crew members were isolated and none so far displayed symptoms of COVID-19, the disease the coronavirus may trigger. They were being tested again, with initial results returning negative.

The Maltese-flagged Mein Schiff was the first to return to Greek waters after coronavirus measures were implemented in March, docking at Iraklio in the middle of September.