HMNZS Manawanui sinks
The HMNZS Manawanui sinks in Samoa. New Zealand Navy

An investigation is underway after a Royal New Zealand Navy ship ran aground and sank off Samoa while conducting a reef survey.

The Royal New Zealand Navy Ship HMNZS Manawanui grounded near the southern coast of Upolu, Samoa, Saturday evening while conducting a reef survey, the New Zealand Defense Forces said.

The 75 crew and passengers boarded lifeboats and "numerous" vessels and a Royal New Zealand Air Force P-8A Poseidon aircraft were deployed to assist.

"Rescuers battled currents and winds that were pushing the life rafts and sea boats toward the reefs, and swells made the rescue effort particularly challenging," the New Zealand Defense Force said.

"We are very grateful for the assistance of everyone involved, from RCCNZ who coordinated rescue efforts, to the vessels which responded and took our crew and passengers from Manawanui to safety," Maritime Component Commander Commodore Shane Arndell said.

At 6:40 a.m. Sunday, the Manawanui was listing with visible smoke, and by 9 a.m. it had capsized, ultimately sinking below the surface.

A C-130J aircraft was deployed to Apia on Sunday evening, carrying medical and welfare personnel, a dive team and light clean-up equipment. The aircraft is set to return to Auckland on Monday with 72 of the rescued crew and passengers. They will be staying at a defense facility overnight for debriefings and are expected to be reunited with their families on Tuesday.

Three remaining passengers from another agency are returning to New Zealand on Tuesday on a commercial flight, officials said.

Chief of Navy, Rear Admiral Garin Golding said New Zealand is responding to support the Samoan government to determine possible environmental impacts from the incident and mitigate them.

"There are assessment teams with specialist skills from a range of agencies who are supporting this response," Golding said.

The cause of the grounding is unknown, officials said. Authorities are initiating a Court of Inquiry into the incident.

The HMNZS Manawanui sailed from Devonport for the Southwest Pacific on Sept. 28, and was scheduled for activities in the Kermadec Islands, Samoa, Tokelau and Niue. It was originally due to return to New Zealand Nov. 1.

Commander Yvonne Gray took command of the ship in December 2022. The Navy said it was the first ship command in her naval career that started in the United Kingdom in 1993.

-With TMX reporting