About 600 anti-oil drilling protesters gathered in Auckland's QEII square in the central city following a hikoi from Cape Reinga.
The crowd swelled as the protest march made its way up Queen St towards Sky City chanting "Statoil go home, leave our seas alone".
Outside the SkyCity convention centre, Greenpeace spokesman Steve Abel said Statoil couldn't continue with its drilling agenda when it faced such large levels of opposition.
"As we stand here today in our hundreds and our thousands, we are in sync with with millions of people around the world."New Zealand had a compelling history of successful protest, including French nuclear testing in the Pacific and anti-apartheid protests, he said.
"Our oceans, we don't want to see them up for grabs."We want to be the first nation where deep-sea oil drilling is banned.
Actor Lucy Lawless told the crowd that although Economic Development Minister Steven Joyce may have reassured Norwegian drilling firm Statoil "not to worry about the natives", they were there to show the firm that "the natives" did not want deep-sea oil drilling in New Zealand.
The New Zealand Petroleum Summit is partly sponsored by Norwegian company Statoil, which in November was granted a permit to test for oil in 9818.88sq km of the Northland Basin.
The hikoi set off from Cape Reinga on Saturday and spokeswoman Hinekaa Mako said: "Leave our seas alone. We want to send a message to all the oil companies there that we are opposed to deep-sea drilling."
Ms Mako said they had received support from iwi as far away as Taranaki, as well as encouragement from Australia. She said about 30 to 40 people were travelling in convoy down to Auckland, where they expected to see hundreds more.
"We have a Facebook page set up and about 500 people have said they're coming," she said.
Rueben Taipari Porter, a kaitiaki of Te Rarawa, said they welcomed Norwegian people to Northland but not the oil companies.
"It shocks us to think that Norwegian people would put this beautiful sea that we catch our food from, beaches that our children grow up on, at risk," he said. "For what? More money?"
Statoil is one of the companies sponsoring the conference, held by Petroleum Exploration and Production Association of New Zealand. The major sponsor of the event is New Zealand Petroleum and Minerals, the Government department that manages the Crown Mineral Estate.