A Royal New Zealand Navy ship has gone aground and sank 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.

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”.

Commodore Shane Arndell, the maritime component commander of the New Zealand Defence Force, said in a statement that several vessels responded and assisted in rescuing the crew and passengers, who had left the ship in lifeboats, Reuters reported.

Those rescued “are being supported in Samoa or on supporting vessels”, he said. A Royal New Zealand Air Force P-8A Poseidon was also deployed to assist in the rescue.