An oil spill is “highly probable” from a grounded New Zealand navy ship which sank and caught fire off the coast of Samoa, the Pacific island nation’s acting prime minister said on Sunday.

Officials in Samoa are conducting an environmental impact assessment in the area where the ship sank on Sunday morning, acting Prime Minister Tuala Tevaga Iosefo Ponifasio said in a statement.

All 75 people on board the HMNZS Manawanui were taken to safety on life rafts in “challenging conditions” and darkness, New Zealand’s Chief of Navy Rear Admiral Garin Golding told reporters.

Those on board included civilian scientists and foreign military personnel, Rear Admiral Golding said.

Authorities in Samoa said some were treated for minor injuries.

The vessel was about a mile from shore when it grounded on a reef and began taking on water, but it took the first survivors five hours to reach land, he said.

New Zealand will hold a court of inquiry into the loss of the ship, which was one of nine in its navy. The cause of the sinking is not known.

The specialist dive and hydrographic vessel has been in service since 2019. It was surveying a reef off the coast of Upolu, Samoa’s most-populated island when it ran aground on the reef.

Photos and videos taken from the shore appeared to show the ship listing before disappearing completely below the waves, with a large plume of smoke rising where it sank.

Defence minister Judith Collins said she did not expect the vessel could be salvaged.

“This is a ship that unfortunately is pretty much gone,” she told reporters.

There was “a lot of fuel” on the ship and efforts had turned to assessing the potential environmental impact, Ms Collins told Radio New Zealand Monday. New Zealand “would obviously have to front up” if there was a spill, she added.

The state of New Zealand’s ageing military hardware has prompted warnings from the defence agency, which in a March report described the navy as “extremely fragile,” with ships idle due to problems retaining the staff needed to service and maintain them.

Mr Golding said the HMNZS Manawanui underwent its usual maintenance before the deployment, adding the ship’s captain was an experienced commander who had worked on the vessel for two years.