Five Greenpeace activists are occupying the Earth Sciences-owned research vessel theTangaroa in Wellington harbour, in protest against deep sea mining.

Greenpeace says an activist dressed as US president Donald Trump flew an American flag, while another held a banner saying 'Don't Mine the Moana'.

Spokesperson Juressa Lee said the boat has just returned from the Clarion-Clipperton Zone in the Pacific, between Hawaii and Mexico, where it surveyed deep sea minerals for the company Glomar Minerals.

Lee said they did not want a state-owned vessel being used for commercial exploration of the seafloor, and warned seabed mining could be used as part of a US government plan to stockpile minerals for military purposes.

RNZ has approached Earth Sciences for comment.

Resources Minister Shane Jones said Greenpeace was trying to scare people, and the boat can be used for mineral research.

Police said they were aware of the protest activity and were engaging with those involved.

American seabed minerals company Glomar Minerals earlier said a team from their subsidiary UK Seabed Resources (UKSR) left Tahiti on 29 July to head to the Pacific Clarion-Clipperton Zone to survey for polymetallic nodules in its license area.

It was running the 65 day survey with Earth Sciences NZ, on the RV Tangaroa, which it said was "one of the most capable deep ocean research vessels in the world".

"UKSR's two International Seabed Authority CCZ license areas cover approximately 133,000 km² of deep seafloor, an area comparable in size to Louisiana, covered in polymetallic nodules containing manganese, cobalt, nickel, copper, and rare earths in a single ore," the company said.

The research was "moving the company closer to the integrated dataset needed for commercial recovery".

The research findings would be shared, adding to Glomar's record of transparency and contributions to marine science, chief executive Chris Williams said.

Earth Sciences was formed last year when NIWA and GNS science merged.