Government and environmental agencies in Samoa are on alert after a New Zealand Navy ship caught fire and sank off the south coast of Upolu.

The HMNZS Manawanui - a specialist dive and hydrographic vessel - was conducting a reef survey when it hit the reef on Saturday night.

Seventy-five crew and passengers were taken off the vessel by liferafts and other boats which came to the rescue.

Samoa fire commissioner Tanuvasa Petone said the ship caught fire and sank on Sunday morning after a successful rescue. Three on board needed hospital treatment, he said.

"They're all on land. They are safe and sound apart from just a few individuals that… have some minor injuries, and so we treated them at the site and transferred to them to the hospital."

Petone said the conditions were "quite rough and windy".

The Defence Force will reveal more information on Sunday afternoon.

Research vessel HMNZS Manawanui, the navy's specialist dive and hydrographic vessel, regularly conducts tasks across the Pacific.

In 2018, the government said the ship would cost $103 million to buy and convert. It was completed in 2019.

Marinetraffic.com's ship tracker earlier showed the vessel was 'aground' near the village of Siumu, on the southern side of Upolu, at 10.45pm Saturday.

Samoa Fire and Emergency Services Authority staff rescue crew of the HMNZS Manawanui after it ran aground in Samoa. Photo: Samoa Fire and Emergency Services Authority

Maritime component commander Commodore Shane Arndell said the grounding occurred while conducting a reef survey.

The 75 crew and passengers were at first evacuated onto life rafts, before being taken ashore by rescuers.

"They are being supported in Samoa or on supporting vessels," Arndell said.

"The New Zealand Defence Force worked closely with Maritime New Zealand's Rescue Coordination Centre (RCCNZ) which coordinated rescue efforts. Several vessels responded and assisted in rescuing crew and passengers. A Royal New Zealand Air Force P-8A Poseidon was also deployed."

The HMNZS Manawanui, aground in Samoa. Photo: Profile Boats / supplied

Photographs uploaded by the Samoa Fire and Emergency Services Authority showed crew being carried into ambulances and life rafts being hauled ashore. People appeared generally to be in good spirits.

Samoa Fire and Emergency Services Authority staff rescue crew of the HMNZS Manawanui after it ran aground in Samoa. Photo: Samoa Fire and Emergency Services Authority

HMNZS Manawanui departed Auckland's Devonport naval base for the Pacific on 29 September.

According to the Defence Force website, the ship has a core crew of 39. It has been in service since November 2019 and has a top speed of 14 knots (26km/h).

In November 2023, it was used in a seven-week operation to conduct underwater surveys and help to dispose of submerged World War II bombs in Niue, Fiji and Vanuatu.

"Some of our crew hail from Pacific nations and so for them our deployments to the Pacific are a way for them to give something back to their communities," Commanding Officer Yvonne Gray said at the time.

This story was originally posted by RNZ News