Act leader Rodney Hide says his party is "shocked and appalled" at the Government's decision to support the United Nations' Declaration on the rights of Indigenous Peoples.

In Parliament he described Prime Minister John Key as "naive in the extreme" that the Government's decision would have no practical effect.

He also criticised National for what he saw as a breach of the "no surprises" policy.

Maori Affairs Minister Pita Sharples flew to New York without publicly revealing he was to make a speech announcing New Zealand would sign up to the Declaration on the Rights of Indigenous Peoples.

The previous Labour Government had refused to sign, saying it was incompatible with New Zealand's constitution, legal framework and the Treaty of Waitangi.

Also it raised concerns that indigenous people would have more rights than the non-indigenous.

The declaration recognised the rights of indigenous peoples to self-determination, to maintain their own languages and cultures, to protect their natural heritage and manage their own affairs.

New Zealand was, until now, one of only four UN member states opposed to the declaration, and Dr Sharples said that had been "a great disappointment" to Maori.

The Government attached a statement to the declaration making it clear that New Zealand was committed to the common objectives of the declaration and the Treaty of Waitangi and that existing legal and constitutional frameworks that underpinned New Zealand's legal system would define the bounds of engagement with the declaration.

Mr Key told reporters this morning the Government sought extensive legal advice before taking the step.

"The practicalities are when we read out our affirmation statement we made it quite clear that nothing in the statement supersedes our laws or our constitution...it's a non-binding aspirational goal...But in a practical step our existing legal frameworks and constitution remains."

New Zealand had a proud record on indigenous rights, he said, and it was an appropriate step to take especially as many of the countries that had signed it had poorer records than New Zealand.

Mr Key said it "was a nice touch" Dr Sharples was able to make announcement at UN when asked about the secrecy around the visit.

A reporter in Canada, from where Mr Key just returned, had asked him about the declaration. Mr Key said it had not been affirmed, even though the Government had decided it would be.

Labour leader Phil Goff said the declaration was signed in secrecy and Dr Sharples had "sneaked off" to New York.

"New Zealanders should have been told first that this was the intention of the Government, they should not have been told afterwards".

Mr Goff said there was a conflict between Dr Sharples' view of the declaration that there were no caveats, and the Government's position about it not making any practical difference.

Labour had opposed the declaration which had unrealistic goals such as returning all land back to indigenous people.

Mr Goff could not see the point in signing up to a declaration that the Government did not intend to fulfil.

"Why would you sign up to something you never intended to act on and you don't actually believe in... They are signing up to something they don't believe in and never intend to implement. The Maori Party has been duped again."

Mr Key said for a long time the Government had made it clear it wanted to affirm the declaration and there had been "no secret" about that.

Dr Sharples, also a Maori Party co-leader, said after negotiation his party and the Government had come to a position they could both accept. He previously expressed concerns about the number of caveats the Government wanted to attach but today seemed happy with the final outcome and was pleased with the standing ovation his speech received at the UN.

Dr Sharples said the Government had agreed to review the status of the Treaty in the constitution and that was about to happen.

Mr Key said the idea of including Treaty into a written constitution was something the government was "a long way away" from considering.

Dr Sharples reflected well on the relationship between the National and Maori parties.