Three Greenpeace activists who padlocked themselves to a ship in New Plymouth have been arrested.

The activists boarded the support vessel the Mermaid Searcher just after 8am today.

Three people, including two who were chained to one of the ship's barriers, have been escorted away by police. Two activists who chained themselves to a much higher pole are still on board.

The ship is at Port of Taranaki to get supplies for the Amazon Warrior, a 25m ship in New Zealand waters on behalf of Austrian oil giant OMV.

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Greenpeace climate campaigner Amanda Larsson says two protesters at the top of the Mermaid Searcher's main post have dropped a banner, while two others "secured themselves" to other parts of the ship.

Larsson said the Amazon Warrior was blasting thousands of square kilometres of the New Zealand seabed in search of oil and gas that were fuelling climate change.

"By stopping the resupply vessel, we're impacting the Amazon Warrior's search for oil and gas in New Zealand's pristine ocean," she said.

"The Amazon Warrior will do whatever it can to avoid coming into port because it knows it will face strong opposition by the public."