International law experts say New Zealand could be off the hook when it comes to the cost of the HMNZS Manawanui cleanup.

He told Pacific Media Network that this was because of a loophole in global environment law, but has urged the New Zealand government to take responsibility.

The navy ship sank off the coast of Upolu a little over a week ago after running aground on a reef.

International law expert Al Gillespie said the difference between a commercial and private vessel or a military vessel is where the issue becomes murky.

“If this was a civilian vessel the obligation is on the country responsible for that vessel to make sure all of the damage is paid for, that there is recompense for the oil and also any other problems that come out from the sunken vessel in addition to removal of the wreck is clear,” he told PMN.

“The problem you've got is that this is a military vessel, and those same obligations in terms of responsibility for the oil and the bunker oil and also responsibility for the salvage is not so clear.”

Auckland University of Technology law professor Paul Myburgh said there are overlapping laws due to the vessel carrying out a number of different tasks.

“As an NZDF vessel engaged in governmental activity, the HMNZS Manawanui is subject to the doctrine of sovereign/State immunity,” he said.

“This means that the ship (and all similar vessels worldwide) are excluded from these conventions and that the ship is not subject to normal maritime legal process or enforcement of maritime claims.

“Any salvage, cleanup operations, or compensation for pollution are therefore likely to be primarily dealt with by inter-governmental and diplomatic negotiations and arrangements.

“As non-military personnel (scientists) were also on board, there may technically be a jurisdictional overlap with the Transport Accident Investigation Commission, but the investigation is more likely to be left up to the Naval inquiry.”

Myburgh said the findings from the inquiry could have legal implications.

"Ultimately, if it were to be proven in the naval inquiry or other investigations that the grounding was caused by negligence, those affected by marine pollution might have a cause of action in tort against the NZ Government under the Crown Proceedings Act."

Affected locals have expressed dissatisfaction with the speed and effectiveness of the responses of both the Samoan and New Zealand governments. Myburgh said all eyes will be on how the response is navigated by those involved.

"Unless the NZ government acts swiftly and decisively to eliminate, or at least mitigate, marine pollution caused by the wreck, this incident has the potential to significantly strain relations between the two countries.”

Speaking to William Terite on Pacific Mornings, Gillespie said although there’s legal ambiguity, New Zealand must take responsibility for political and ethical reasons.

“The economic costs involved in this are huge, in terms of not just if the bunker oil breaks out, the costs of the cleanup could be in the tens of millions.

“And if the ship itself needs to be salvaged in the tens potentially even up to 100 million, the cost of the ship.”

Gillespie said New Zealand has to listen to the people to preserve the critical relationship towards Samoa.

“If those communities want that wreck removed, New Zealand must take that responsibility, pay for all of the associated costs and consider recompense for the damage done.

“That relationship with Samoa is vital, because if we don't take up that responsibility, you will find other countries in the region will come in and offer to remove it probably for no cost, but for the political influence that they could win.”