A Royal Caribbean ship has returned to Singapore on day three of a four-day "cruise to nowhere" after a passenger tested positive for Covid-19.

The city-state's "cruises to nowhere" - starting and ending at the same port without stops - launched last month.

They are an attempt to revive the hard-hit industry, which largely ceased worldwide after outbreaks on board but have since resumed in a few places.

Singapore's special cruises were only open to its residents.

The Royal Caribbean cruise ship Quantum of the Seas departed Singapore on Monday for a four-day round trip as part of a "safe cruising" pilot programme announced by the country's tourism board in October.

The cruise company said it had turned the ship around after one guest tested positive for coronavirus after checking in with the on-board medical team.

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"We identified and isolated all guests and crew who had close contact with this guest, and each of those individuals have subsequently tested negative for the virus," it said in a statement.

It said guests would be allowed to disembark "after a review of contact tracing is completed".

A raft of safety measures were introduced for passengers on the special cruises to nowhere, including coronavirus tests before boarding and after disembarking. The ships were also running at half their usual capacity for safe distancing purposes.

"That we were able to quickly identify this single case and take immediate action is a sign that the system is working as it was designed to do," said the Royal Caribbean.

An 'uncertain future' for cruise operators

By Andreas Illmer, BBC News, Singapore

Singaporeans are desperate to get off their little island. For months, the border has been effectively closed and the thirst for travel has taken bizarre forms like eating airline food on a plane parked on the tarmac or booking staycations at the airport.

An eagerly awaited travel bubble with Hong Kong was delayed because of rising cases over there.

So the 'cruises to nowhere' were the first real travel option in a very long time - and the initial trips all sold out in no time. Returning guests were beaming with praise and enthusiasm, both about the cruise experience and the safety protocol.

After all, in the early days of the pandemic, cruise ships had been hotbeds for the virus, sometimes stranded for weeks at sea with those on board not allowed to get off. But Singapore has had only a handful cases over the past few months and people put a lot of trust in the authorities' stringent contact tracing.

The Covid case on the Quantum of the Seas will put that trust to the test and cruise operators once again are facing a very uncertain future.