Meanwhile, the Labour Party says the eyes of New Zealand's partners will be on what happens next, with the Prime Minister set to attend an all-of-Commonwealth summit later this month - which happens to be in Samoa.

The Manawanui sank off the south coast of the island of Upolu on Saturday, after running aground, catching fire and capsizing.

The immediate focus was on the safety and recovery of its crew, with attention now turning to salvage and environmental mitigation.

Brent Ross runs Offshore Adventures, a surf adventure company on Upolu's south coast, and his backyard now has an unwanted landmark.

"It was quite bad. Yeah, it was sad to see," he said.

He told RNZ Pacific that he could see debris from an opened shipping container and "a lot" of fuel oil. He was concerned not just for his livelihood, but for local fishermen, and Samoa's entire marine environment.

"Seeing how much fuel was out close to the wreck, it's got to go somewhere. I imagine that's going to end up on the beaches. The local fishermen, Samoa is very much still subsistence lifestyle for a lot of people. You know, they go fishing at night to feed their families. I worry about them," he said.

 READ MORE

• Navy ship may have lost power before running aground, Collins says
• Manawanui sinking: Crew and passengers returning to New Zealand
• Defence Minister: ‘This is a ship that, unfortunately, is pretty much gone’
• HMNZS Manawanui: What we know about the Navy ship's sinking

There is still a mountain of contingencies to determine just how damaging the Manawanui's sinking could be.

These include whether the sea floor is rock or sand; how deep the water was; the weather conditions; how much of the reef the ship scraped past; exactly what chemicals were onboard; what state the hull was in; and how clean it was.

Coastal science Professor Chris Battershill, who helped lead the Rena cleanup and recovery, said while there were many unknowns, the quicker agencies acted, the better.

"Unlike some of the other experiences internationally, where ships have wiggled their way across an entire shoaling platform of coral, here it's been a relatively short, from what we understand, transition from the reef and then down into deeper water," he said.

"So once there, of course, with the oil coming to the surface that then presents a problem of slicks coming ashore if there's an onshore wind. Ordinarily if it ends up on a beach that can be taken away, along with contaminated sand. The only consideration that does cause concern is if at low tide there's an area of shallow-water reef that's exposed with an onshore wind, then the slick will engage with that part of the reef and will do some damage."

The Defence Force said the Manawanui carried several marine-standard chemicals onboard like cleaning products and emission control (marine urea solution), and that there were no hazardous chemicals onboard "beyond those that would be carried by most commercial ships."

It also said the Manawanui was fuelled with Automotive Gas Oil, a light oil commerical diesel commonly used by commercial and military vessels.

Battershill said the lighter oil can evaporate off its more toxic short-chain hydrocarbons relatively quickly compared to heavy oil.

"So if they evaporate off, that leaves larger-chain hydrocarbons on the slick, which are relatively less toxic. And the environment, just depending on how much was released over how long a period, can tolerate that to some extent," he said.

"If a slick arrives onshore, there'll be an area of immediate inundation and smothering and contamination. But what we learned from the Rena is if that load can be taken away from the system, as was done in the Rena event by a very large volunteer army, then the environment has a chance to recover. We saw recovery of kaimoana along the beaches in the Rena situation within about three to four months."

The Defence Force said the Manawanui had the equivalent of third-party insurance, for things like salvage or cleanup, but not a replacement.

"The ship itself is not covered for insurance, as historically RNZN vessels were not insured due to the prohibitive cost. Even if purchased, policies are heavily limited by exclusions and conditions that apply to many activities our Navy operate in, such as shallow waters and cyclone responses," a spokesperson said.

While Budget documents show the Defence Force has reduced some spending on insurance, the Defence Minister's office told RNZ there had been no reduction in insurance for the Manawanui.

Labour's defence spokesperson Peeni Henare said with a new defence capability plan on its way, better insurance should be looked into in the future, especially with the two frigates Te Kaha and Te Mana reaching the end of their life expectancy.

"When we purchase things like a house or a car, that's why you have insurance. And if we're going to look towards replacing such an important piece of infrastructure, I would have expected that we have better than third party insurance," he said.

Later this month, the heads of government from every Commonwealth nation, and the head of the Commonwealth King Charles are all meeting in Samoa for the biennial CHOGM summit.

It will be the Prime Minister's first CHOGM. Henare said New Zealand's partners hold the Defence Force in high regard, and all eyes would be on the response.

"This particular incident certainly will cast a bit of shade on the way that the world looks at us," he said.

"The fact that the cleanup and the salvage, the details are a bit slim at the moment, and with all the world watching, it's important that we do a good job here."