Hundreds of Covid-19 cruise ship passengers who spent last week travelling around New Zealand are today going into self-quarantine at home across the Tasman.

Majestic Princess arrived back in Sydney this morning after a 12-day cruise around New Zealand, which included time on shore in Dunedin, Christchurch, Wellington, Auckland and the Bay of Islands.

An estimated 800 of the combined 4600 passengers and crew have Covid-19, with University of Otago professor and New Zealand epidemiologist and local Covid-19 expert Michael Baker describing it as a “major outbreak”.

The ship and its passengers spent their last day in New Zealand in and around Russell and Paihia on Wednesday; with excursions including to the markets at the Paihia Village Green.

Some Majestic Princess passengers would have spent up to eight hours onshore in the Bay of Island tourist towns on Wednesday.

Covid-19 cases have been consistently on the rise in Northland over the past month; this week there were 817 new cases reported in the region, up from 780, 646, 479 and 254 over the previous four weeks.

The Ministry of Health has been approached for comment on the ship’s visit despite high Covid-19 numbers.

But Far North District Council deputy Mayor Kelly Stratford – also a Bay of Islands-Whangaroa councillor – said she didn’t believe there was any reason for alarm, saying Covid-19 was already spreading through the community.

She added retailers in the area had good health and safety practices.

“We’ve already got Covid in our community, it is not from the cruise ships,” Stratford said.

“I am testing just about every day myself because I am coming into contact with people. It is just a way of life.

“I personally expect to get it from somebody coming back from overseas, from whanau we haven’t seen for three years rather than off the cruise ships to be honest. We just have to live with Covid now.”

Talking to the Herald this morning while passengers started disembarking, Baker said he was alarmed at the high percentage of positive cases onboard.

But, he said, international air travel - and not cruise ships – posed the greatest threat to new variants of Covid-19 gaining hold in New Zealand.

“I am not overly worried about cruise ships in that regard, because basically we have open borders now . . . we have around 10,000 people flying into New Zealand every day from around the world,” he said.

“Relative to cruise ships, that is a much bigger number.”

Baker described the number of people infected on Majestic Princess as “quite a major outbreak”.

He added the high spread was “shocking”.

“That is a very high attack rate. It’s almost 20 per cent infected . . . that is a very high proportion infected,” he said.

“That goes back to the early stages of the pandemic when they had a very high attack rate on these ships. Cruise ships just didn’t know how to deal with the infection.”

He said the rapid spread of the virus through those onboard the boat should be viewed as a “warning” to any New Zealander who was considering cruise ship travel.

Mandatory Covid-19 vaccinations and pre-departure testing are no longer required on most cruise ships.

Princess Cruise Lines’ website states that on Majestic Princess, like its other ships: “All guests are welcome – regardless of vaccination status.”

Once onboard, any traveller who tested positive would then face a five-day isolation stay in their cabin.

That was a timeframe Baker said was “really quite short”, adding: “A lot of people will still be infectious, and infected, after five days . . . we know that”.

The widespread absence of mandatory vaccinations and pre-departure tests meant cruise ships were now “more vulnerable for outbreaks on board” such as those seen on Majestic Princess.

That should be of concern for elderly or vulnerable New Zealanders considering a cruise, Baker said.

While cruise ships were like a “small floating town”, they would have limited healthcare facilities.

“They won’t have ventilators and they will have limited oxygen,” he said.

If Covid-19-positive passengers’ health badly deteriorated, it would lead to a “very difficult evacuation in the middle of the ocean”.

“The biggest concern I have is around the health of people onboard,” Baker said.

“Often, they are going to be an older less mobile demographic.

“You’ve got thousands of people basically in a very contained environment. While they may spend some time in well-ventilated areas like a deck outdoors, most of the time they are mixing indoor environments which are quite confined with lots of other people.”

Last month, fellow cruise ship Ovation of the Seas docked at several New Zealand ports while a much smaller number of travellers had Covid-19.

More than 130 cases were reported out of the 4500 passengers and crew onboard.

Health authorities were informed of the cases on board that ship, but they were satisfied with quarantine measures put in place Ovation of the Seas, meaning other passengers could disembark.

Baker said the number of reported Covid-19 cases on Ovation of the Seas was “quite a manageable number” compared to those from Majestic Princess.