The two guests, who shared a stateroom, are asymptomatic and have been placed in isolation, Celebrity said in a statement.

The cases were identified through routine testing ahead of the ship’s departure from St Maarten on Saturday (5 June).

Millennium is sailing a seven-night itinerary, calling in Barbados, Aruba and Curacao. Around 500 passengers are onboard, in excess of 95% of whom are fully vaccinated against Covid-19.

All crew are also required to be fully vaccinated.

"We are conducting contact tracing, expediting testing for all close contacts, and closely monitoring the situation," said Celebrity.

The line added the situation was proof its health and safety protocols were working. It is unclear whether those who tested positive were among the small proportion of guests not fully vaccinated.

Celebrity said they were being monitored by the ship’s medical team.