About 30 environmental protesters have stormed an Austrian oil company's support ship in Timaru to prevent it leaving port.
The Bahamas-flagged OMV was preparing to leave the Port of Timaru and travel north to the oil rig off the coast of Taranaki.
Greenpeace said OMV was about to begin drilling three oil wells there.
Police said they were called to the port at about 6am.
They said officers were on site to ensure safety and to uphold the law while recognising the lawful right to protest.
Climate and energy campaigner Amanda Larsson said those taking part in the occupation were 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 were also involved.
