Greenpeace protesters aboard a Shell oil-drilling ship, including actor Lucy Lawless, are battening down for a windy night.

The group boarded the ship at Port Taranaki, about 7am on Friday, and scaled its 53m drilling tower in an attempt to stop it sailing to the Arctic.

Strong winds were battering the tower on Friday night and the protesters had pulled down their banner.

"Wind strengthening. Taking the shredded banner down. Fasten your seatbelts, Muchachos, it's going to be a bumpy night!" Ms Lawless tweeted.

In a blog, Ms Lawless said it was scary climbing the high tower, but she was safe and securely fastened.

"I think I'd rather be home with a latte, but I don't feel that I had a choice."

An oil spill in the Arctic could last for years because the location was so remote, she said.

"The plankton that prop up the whole ecosystem would die and the ripple effect would be heinous."

A Greenpeace spokesman told NZ Newswire the group had enough gear to stay for several days and all of them planned to stay for as long as possible.

The Noble Discoverer, a Shell-contracted ship, is due to depart to drill three exploratory oil wells in the Chukchi Sea off the coast of Alaska, Greenpeace says.

Police arrested one person at the port's gates on Friday morning and have spoken with the occupiers.

Inspector Blair Telford said police had met with the owners of the ship and agreed the protesters would be left where they were for now.

"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."

Safety was paramount and "we won't needlessly jeopardise the safety of our staff, the crew of the ship or the protesters," he said.