The police have left the Shell drilling ship Noble Discover, while Greenpeace protesters, including Lucy Lawless, prepare to spend the night onboard.
Earlier today five police officers boarded the ship and told the protesters they were under arrest, Greenpeace spokesman Nathan Argent said.
But the activists, including actress Lucy Lawless, told police they had a moral obligation to stay.
Protesters climbed aboard the Noble Discoverer in Taranaki at about 7am in an attempt to stop it from sailing to the Arctic.
Police said tonight that following a series of meetings with the ship's owners and the Port, they had agreed "at this stage" to not force the protesters to move.
But they would continue to monitor the situation and would immediately respond if the protesters descended from the drilling tower.
"Although the protestors 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."
There would be increased security at the Port tonight, Telford said.
Meanwhile, the protesters are determined to stay on board long enough to stop the ship sailing, one Greenpeace activist said.
"The guys are well equipped and have enough food to last a couple of days and gear to protect them from the weather," he said.
"We don't plan to leave until Shell agrees to stay out of the Arctic."
He said the protesters were being supported by other Greenpeace members in New Plymouth at an undisclosed location.
Meanwhile, police cars continue to patrol near the port.
One person has been arrested after Greenpeace protesters, boarded the Shell drilling ship bound for the Arctic.
Police confirmed that a man, who was not onboard the ship, had been taken into custody after being arrested at the port gates.
Access to Port Taranaki is being controlled but the port itself remains open, a police spokeswoman said.
Shell spokeswoman Shona Geary said they were disappointed Greenpeace had chosen this method to protest.
"Actions such as this jeopardize 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.
The Noble Discoverer was 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, Greenpeace said.
Lawless and the others had scaled its 53-metre drilling tower and were hanging banners from its summit, reading "Stop Shell" and "SaveTheArctic".
The Xena star, who has long campaigned for environmental issues, said she was taking part on "behalf of the planet and her children".
"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.
"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," Lawless said.
Greenpeace New Zealand Climate campaigner Steve Abel said an oil spill would devastate the Arctic.
"There is no more striking an emblem of the madness of oil expansion than the struggle for the Arctic.''
A Shell spokeswoman said the ship was due to leave this weekend for the Alaskan coast to drill over the northern hemisphere's summer months.
Shell was investigating the situation at the port and were yet to decide what action to take. They were not seeking police help at this point.
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