Cruise ship Viking Orion was restricted to visiting approved ports and asked to leave New Zealand waters because of algae on its hull, says the Ministry for Primary Industries - MPI.

The space-themed Viking Orion is due to visit Tauranga on January 17 according to the Port of Tauranga website, and first docked in New Zealand for the current cruise ship season in mid-December.

Biosecurity New Zealand environmental health manager Paul Hallett says approved ports can manage risk better than special marine environments, like Fiordland.

"Approved ports have regular surveillance, our teams are based there, and ships stick to regular vessel pathways," he said.

Despite the restricted status, Viking Orion still visited commercial ports in Dunedin, Christchurch, Wellington, Napier, Tauranga and Auckland.

But Hallett said the ship was given a final departure date.

"Because of the level of algae and barnacles, the vessel was asked to depart New Zealand waters by 29 December. The vessel operators chose to leave Wellington after visiting it on 26 December, to have its hull cleaned in Australia."

The algae and barnacles, or biofouling, was picked up during regular Biosecurity NZ risk assessment and surveillance.

A Viking spokesperson said "a limited amount of standard marine growth [was removed] from the ship's hull in a routine cleaning procedure for nautical vessels".

The ship had to miss several stops on its scheduled itinerary "in order for the required cleaning to be conducted".

"Viking is working directly with guests on compensation for the impact to their voyage," the spokesperson noted, but declined to comment further.

It was believed the cruise missed three stops in Christchurch, Dunedin and Hobart.

Viking Orion was expected to arrive in Melbourne on January 2.

Viking Orion arrives in Australia

Hundreds of passengers have been stranded on a cruise ship floating off Australia's coast after a fungus was found growing on its hull and it was denied entry to Christchurch.

The Viking Orion was reportedly denied permission to dock in Adelaide after authorities discovered a "marine growth" on the ship.

Australia's fisheries department said the fungus - which it called biofoul - was "potentially harmful".

Officials said the ship's hull must be cleared before entering the country.

Biofoul is an accumulation of microorganisms, plants, algae, or small animal and can allow the importation of invasive species into non-native habitats.

The fisheries department said the management of fungus was a "common practice for all arriving international vessels" and said that the ship had to be cleaned to avoid "harmful marine organisms being transported" into Australian waters.

"Professional divers were engaged directly by the vessel line/agent to clean the hull while at anchor outside Australian waters," it said.

One passenger wrote on Twitter more than 800 guests remained onboard, many of whom were "upset and angry" by the company's "negligence".

The 14-deck, 930-person ship - which was built in 2018 - had reportedly dropped anchor about 27km off Australia's coast while the cleaning is done.

In a statement, operator Viking admitted a "limited amount of standard marine growth" was being cleared from the ship's hull and said that this had caused the vessel to "miss several stops on this itinerary".

But the operator said it expected to sail toward Melbourne shortly, where it would dock on Monday.

"Viking is working directly with guests on compensation for the impact to their voyage," it said.

In a letter on Friday, the ship's captain apologised that "the current cruise falls short of your expectations" and said a member of Viking's customer relations team would make an "adjusted offer of compensation" to guests in the coming days.

Marine pests

Hallett confirmed the Viking Orion posed less of a risk than the Coral Princess, which had to have snails cleaned off the underside of the ship off the coast of Tauranga a week earlier.

"We know that nearly 90 per cent of marine pests arrive in this country on the submerged surfaces of international vessels," he said.

"Such pests can adversely impact New Zealand's economy and environment. This is why New Zealand has some of the highest biofouling standards in the world.

"Some don't have any or minimal impact, but others can cause issues with our marine life, especially in sensitive areas like Fiordland and to commercial industries such as mussel farming."

High-risk organisms associated with biofouling include bivalves, such as mussels and oysters, foliose algae, hydroids, tunicates, sponges, and mobile organisms like crabs and starfish.

Inchcape-McKay Shipping managing director Craig Harris said it was unusual to see cruise ships needing to be cleaned.

He believed the lay-up of ships during the pandemic may be part of the problem.

"They are generally dry-docked and have their hulls cleaned and painted. At the moment, there's a shortage of facilities all around the world of underwater divers or cleaners.

"My suspicion is that's the reason why the ships just have not been able to comply fully."

It was the first time Harris remembered cruise ships being cleaned in New Zealand as they were normally cleaned to a high standard.

Cargo ships were often cleaned, sometimes multiple times a week, he said.

According to MPI, 6121 international vessels arrived in New Zealand between January 2020 and September 2022.

There were 377, or 6 per cent vessels that were issued a notice of direction to address biofouling issues.

Niva Chittock/RNZ

Further reporting: RNZ