Police have arrested six climate change protesters who allegedly tried to stop a coal ship leaving Lyttelton Harbour.
Despite the efforts of Greenpeace activists the Hellenic Sea began its departure from Lyttelton Port about 7.25pm.
Greenpeace's Rainbow Warrior II earlier anchored in front of the 225m ship, which is loaded with 60,000 tonnes of coal bound for export from the state owned Solid Energy mining company.
The Harbour Master boarded and took control of the Rainbow Warrior and a Lyttelton Harbour tug was used to push the boat across the water to allow the Hellenic Sea to depart.
Three protesters who allegedly attached themselves to the hull of the Hellenic Sea and three onboard an inflatable involved in the action have been taken into custody, Greenpeace said.
Greenpeace spokesman Simon Boxer said the protesters' efforts were still being viewed as a success.
"We would have liked to have seen it stopped, but they have used quite forceful methods.
"The main point was really to highlight that these shipments are increasing and the mining of coal is increasing and the path that New Zealand is on."
Dozens of people gathered on roads overlooking the port as the drama unfolded earlier this evening.
Protesters clambered onto the hull of the Hellenic Sea to unfurl a banner on the vessel reading "Target climate change" in reference to their national campaign against global warming.
They attached themselves with grappling hooks and used interconnected ropes to hang from the vessel.
Crew on board the Hellenic Sea had reportedly tried using hoses to try to force the protesters off the hull.
A lone protester also attached himself to the Rainbow Warrior's anchor rope to prevent it being cut.
Campaign Manager for the Rainbow Warrior Carmen Gravatt said those involved understood they could be arrested but had felt strongly enough about climate change to take the action.
A spokeswoman for Lyttelton's port company, Julie McCloy, told NZPA the Rainbow Warrior had not been due to leave port on its national publicity tour until 7pm, but shortly after 5pm pulled out of its berth without notifying the harbour authorities.
"It left port early, without authorisation, and without a pilot, which is illegal - a breach of local bylaws," she said.
"It was also a breach of maritime safety protocols.
"We tried to ask them to return to port, and they refused and then turned off their radio.
Ms McCloy said that because the vessel had breached bylaws, Greenpeace could be prosecuted, but she declined comment on whether interfering with shipping and boarding a vessel would attract charges of piracy or terrorism.
"We could prosecute them if we chose to," she said.
Greenpeace has called on the Government to introduce stricter measures to halt climate change, including putting a cap on coal exports, halting the expansion of coal mining and strengthening the emissions trading scheme to discourage burning of coal in New Zealand.
- With NZPA