Seven protesters, including Kiwi actress Lucy Lawless, are preparing to spend the night on-board a deep sea oil drilling ship docked in Taranaki.
One man has already been arrested in connection with the anti-oil protests, and police have been talking to the activists on the ship.
They said the protesters will be left alone for now, but police will be keeping a close eye on their actions.
"Although the protesters are breaking the law by being aboard the ship, they are in an isolated location on the ship which allows both the Port and the ship to operate their normal business," Inspector Blair Telford said.
"We have considered various options and we have the skills, capabilities and equipment to deal with all options. However safety remains paramount and we won't needlessly jeopardise the safety of our staff, the crew of the ship or the protesters."
Greenpeace said the protesters climbed a 53 metre drilling derrick on the Noble Discoverer and then chained themselves to the ship's drilling platform.
Greenpeace said the Noble Discoverer is due to depart on a 6,000 nautical mile journey to drill three exploratory oil wells in the Chukchi Sea off the coast of Alaska.
ONE News spoke to a man employed on the ship who said more than 400 people, including many New Zealanders, do shifts on board and he is concerned there will be layoffs if Greenpeace stops it from sailing.
Lawless, who is famous for her role in Xena, said on TVNZ's Close Up said she will stay there as long as she can and is prepared to be arrested for this cause.
I am a true believer in the fact that climate change, if it runs away on us, is going to bring down a terrible future on our children," said Lawless.
As a mother and a human being I find that absolutely reprehensible. I believe we have to clean this up and take care of this burden so our children wont have to
But Shona Geary, Shell's corporate communications manager, said the company is disappointed that Greenpeace has chosen this method to protest, saying it jeopardises the safety of everyone involved.
"While we respect the right of individuals to express their point of view, the priority should be the safety of Noble Discoverer's personnel and that of the protesters," she said.
"Shell has taken unprecedented steps to pursue safe, environmentally responsible exploration in shallow water off the coast of Alaska."
Shell believes there could be 27 billion barrels of oil in the Chukchi sea, and has also invested billions of dollars in environmental safety plans.
A promotional video by the company on YouTube claims it is taking every precaution in retrieving the oil despite it being at a relatively shallow depth.
Oil drilling 'unacceptable'
Lawless said oil drilling in the Arctic is "absolutely uncalled for and unacceptable" and "ordinary people" like her have to stand up and say no.
"Deep-sea oil drilling is bad enough, but venturing into the Arctic, one of the most magical places on the planet, is going too far," Lawless said.
"I don't want my kids to grow up in a world without these extraordinary places intact or where we ruin the habitat of polar bears for the last drops of oil."
The protesters unfurled anti-oil drilling banners reading "Stop Shell" and "#SaveTheArctic" on the ship.
Lawless and the other Greenpeace protesters are equipped with
survival gear and enough supplies to last for several days.