The first Ukrainians boarded the specially chartered M/S Victoria on Tuesday, in a policy that critics brand potentially unsafe and unsuitable.

The Scottish government plans to use the vessel, which is says is "fully staffed" and safe, to house up to 1,700 Ukrainian refugees in 739 cabins until next January to fill an accommodation backlog for refugees.

It insists they will have access to support services, including healthcare and benefits, as well as "unrestricted access" to services onshore.

"We do not want people spending more time in temporary accommodation, such as the ship, for any longer than is absolutely necessary," government minister Shona Robison said.

"But we want to make them as comfortable as possible during their stay and we have worked with partners to provide a variety of services on-board for guests in addition to the support services available."

She noted they include restaurants, child play facilities with toys and books, shops, laundry, cleaning, wifi access and communal spaces.

But opposition parties and welfare organisations have voiced concerns, including over access to schooling for younger refugees and the possibility of Covid-19 outbreaks on-board.

"People fleeing war were promised a safe place to stay in Scotland, but instead they have been stuck on a cruise ship," Scottish Labour's Sarah Boyack said.

Scotland has provided housing for more than 9,000 displaced Ukrainians since Russia invaded Ukraine on February 24.

A sponsor scheme has brought nearly 100,000 Ukrainians so far to Britain, but Scotland suspended its version of the scheme earlier this month after a dramatic increase in the number of new applicants.

It said more time was needed to match new arrivals to temporary and long-term accommodation.

Former finance minister Rishi Sunak -- who is competing with Foreign Secretary Liz Truss to replace outgoing British Prime Minister Boris Johnson -- recently unveiled plans to detain migrants on cruise ships after they crossed the Channel.

The proposal was subject to hostile counter-briefings, with newspapers reporting it was "laughed off the table" by ministers and officials over costs and legal concerns.