A Greenpeace statement quoted Jo McVeagh, one of the 12 activists locked onto the ship, several kilometres off Tauranga, as saying, 'Fonterra's involvement in rainforest destruction and the massive climate impact this causes is criminal.'

Boxer said, 'Fonterra's intensification of the dairy industry is fuelling rainforest destruction, increasing greenhouse-gas emissions here and abroad, putting pressure on the health of our land and threatening our clean, green reputation.'

It was a peaceful protest, he told Radio New Zealand, and the crew and port authorities had been told it was intended to stop the ship unloading its cargo on Wednesday.

Port of Tauranga chief executive Mark Cairns told the New Zealand Press Association that police were on their way to arrest the protesters, and they would not prevent the ship from being unloaded.