All Singapore passengers aged 12 and above who book a Royal Caribbean cruise from today will need to be fully vaccinated when they set sail.

This requirement will apply only to all new bookings made from today, cruise operator Royal Caribbean International announced on Wednesday.

Those who have booked a cruise before today can still sail even if they are not fully vaccinated.

Only two cruise liners - Royal Caribbean's Quantum of the Seas and Dream Cruises' World Dream - are offering trips from Singapore currently.

It is not mandatory for Dream Cruises' passengers to be vaccinated, according to its website.

The two cruise operators were given the green light to offer cruises to nowhere from Singapore under a pilot scheme that started last November.

This came after cruises were halted amid escalating Covid-19 cases.

Under the scheme, the round-trip cruises have no ports of call, and passengers have to take a mandatory Covid-19 test prior to boarding.

Royal Caribbean said of its latest move: "The vaccine requirement is one of the many layers of measures that safeguard the well-being of guests and crew, and Royal Caribbean will continue to evaluate and update its measures as circumstances evolve with various government and health authorities."

Ms Angie Stephen, vice-president of Royal Caribbean International, said that on average, 99 per cent of the guests on its Singapore cruises are already fully vaccinated.

"Children under the age of 12 are not required to be vaccinated and, adhering to the current government restrictions, are allowed to accompany their vaccinated parents to activities, including dining in, as long as they are from the same household, for the duration of the cruise," she said.

"All guests are required to adhere to the recently updated health and safety measures announced last Friday."

At Dream Cruises, even though it is not mandatory to be vaccinated to sail, more than 90 per cent of its passengers since July have been fully vaccinated, said its president Michael Goh, who is also head of international sales at Genting Cruise Lines.

But only guests who have been fully vaccinated are allowed to dine at the restaurants on board World Dream.

Unvaccinated children aged 12 and below can also dine in if they are from the same household as the accompanying adults.

This starts from 11am on the second day of the cruise.

Prior to that, all guests, regardless of their vaccination status, will be allowed to dine in, as they would have undergone the mandatory pre-boarding antigen rapid test.

Those who are not vaccinated can opt to take away their food or call for room service.

Mr Goh said: "Dream Cruises will continue to monitor closely the situation and explore the additional layers of potential safety measures, including guests' vaccination requirements, in the future."