Here's the view from onboard @OMV's oil rig support vessel in Timaru. 30 community activists are still on the ship. By occupying @OMV’s henchboat, we’re delaying their monster oil rig from drilling for new oil in the middle of a climate emergency. #PeoplevsOil#ClimateUprisingpic.twitter.com/AJ6E6sPaTu
Police said they were called to the port at about 6am.
Climate and energy campaigner Amanda Larsson said those taking part in the occupation are prepared to stay overnight.
"By occupying OMV's henchboat, we're delaying the monster rig from drilling for new oil in the middle of a climate emergency," she said.
"OMV's oil rig is almost 50 nautical miles off the Taranaki coast. Its remote location means it's nearly impossible for ordinary New Zealanders to take peaceful action to confront it directly.
"We've brought the resistance here to disrupt its chain of support. We won't let this rig carry out its climate-destroying activities quietly, out of sight and mind."
She said representatives from other environmental groups such as Extinction Rebellion, Oil Free Otago and 350 Aotearoa are also involved.