University of Waikato associate professor in biodiversity and ecology Nick Ling said there was clearly considerable urgency to remove the remaining fuel from the HMNZS Manawanui wreck.

He said this should be done ahead of the Pacific cyclone season.

The NZ Navy vessel sank on a coral reef off the coast of the island of Upolu after running aground and catching fire on October 6. All 75 of its passengers and crew safely evacuated.

Local authorities said about 200,000 litres of diesel leaked from the wreckage in the week following the incident.

Ling told One News he was "somewhat surprised" that a contractor had not been sought earlier in the clean-up process "given that this was always the priority, and that there will obviously be further delay in getting salvage assets to Samoa once a contractor is engaged".

He also expressed concern there "appears to be no ecological monitoring of the site", even as local fishermen reported fish becoming contaminated with fuel days after the wreck.

Ling added that while the NZDF is continuing to monitor the wreck and surrounding coast, it was "unclear whether this relates simply to the presence of debris and oil".

"While the fuel carried on the Manawanui is considerably less problematic than heavier forms of oil such as crude... there is still the potential for chemical contamination of the reef and its fish stocks by toxic hydrocarbons. There will also be other forms of oil on board such as lubricating oils.

"I would have thought the NZ Government owed it to the people of Samoa to undertake whatever work was required to allay fears of the potential or current impacts of the wreck."

Meanwhile, the process to remove fuel from the HMNZS Manawanui after it sank in Samoa is expected to begin this month, the New Zealand Defence Force says.

NZDF senior national representative Commodore Andrew Brown said the Manawanui’s "main fuel tanks remain intact and any small leaks are being managed and contained".

This is contradicting reports of fuel being spotted around the area where Manawanui sank.

Meanwhile, New Zealand’s Health and Pacific Minister Dr Shane Reti said New Zealand’s relationship with Samoa remains strong.

“The Treaty of Friendship is a strong treaty between us and Samoa… and I would say our relationship with Samoa is strong.”

Reti highlighted the Government's focus on mitigating environmental harm and working alongside Sāmoan counterparts to protect the region.

He denied that New Zealand is a bad neighbour and ally to the island nation.

“Our prime goal here now is to protect the environment and be focused on doing everything we can to do that in collaboration with our colleagues and friends in Samoa.”