A Royal New Zealand Navy ship, HMNZS Manawanui, has gone aground and later sunk off Samoa while doing a tropical reef survey but all 75 crew and passengers on board are reported safe ashore.

The New Zealand Defence Force said on Sunday the Manawanui, the NZ navy’s specialist dive and hydrographic vessel, ran aground near the southern coast of Samoa’s main island of Upolu on Saturday night as its crew were making the survey at the island nation.

Samoa fire commissioner Tanuvasa Petone said the ship caught fire and sank on Sunday morning after a successful rescue, NZ Radio reported. 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.” 

The cause of the grounding was unknown and would need further investigation, the Defence Force said. The vessel later capsized and was below the surface by 9am local time on Sunday, New Zealand Defence Force said.

It was “working with authorities to understand the implications and minimise the environmental impacts”.

Chief of Navy Rear Admiral Garin Golding told a press conference in Auckland that a plane would leave for Samoa on Sunday to bring the rescued crew and passengers back to New Zealand.