Maori protesters confront New Zealand PM John Key.

A group of mostly Maori protesters forced New Zealand Prime Minister John Key to retreat from a national day ceremony on Sunday amid rising objections to the planned sale of state assets, Asia One News agency reported.

Key was confronted by the angry protesters as he arrived at the Te Tii Marae, a traditional meeting house in the northern township of Waitangi and he left soon after as chants and yelling drowned out his speech.

The speech was part of ceremonies marking New Zealand's national day and the signing of the Treaty of Waitangi between the British Crown and indigenous Maori in 1840, which paved the way for European colonisation of the country.

Police and Maori wardens kept the crowd of protesters away from Key but they could not stop the chants of "we don't want to listen to you" and "go home".

Key told reporters he did not feel threatened by the protesters but felt the incident was a lost opportunity for dialogue.

"What we really ended up with was a bunch of people with mega-phones that drowned out any chance of a sensible conversation," Key said, adding he left early because the crowd could not hear what he was saying.

Protester Joe Carolan told Fairfax Media the group was battling the sale of public assets.

"This attack is about the people in New Zealand. This is not a battle between the Maori and Pakeha (New Zealanders of European descent), it's between the rich and poor," he said.

Opinion polls have shown the partial sale of state-owned energy companies to be unpopular, but Key is adamant the programme will go ahead.

When his centre-right National Party was returned to power in a general election last November he said the victory confirmed his mandate to sell state assets to prop up a struggling economy.

Although the signing of the treaty marks New Zealand's national day it is often used by Maori activists as an opportunity for protests.

Former prime minister Helen Clark refused to return to the marae after she was jostled by protesters in 2004.