The Maori Party says it's "bitterly disappointed" by Prime Minister John Key's comment that the government will probably ignore a Waitangi Tribunal decision on water rights.

Co-leaders Tariana Turia and Pita Sharples, who are government allies, say it seems to be a unilateral rejection of Maori rights.

The tribunal was on Tuesday in its second day of hearings on an application by the Maori Council for a finding that the partial privatisation of four state-owned energy companies should be put on hold until Maori water ownership claims have been resolved.

Mr Key said on Monday the tribunal's findings weren't binding on the government and could be ignored.

"The government is very firm - no one owns water, we certainly don't believe Maori own water," he said.

The Maori Party co-leaders say Mr Key's comment that "we could choose to ignore what findings they (the tribunal) might have" is very serious.

"To make such comments is an insult to all of us," they said on Tuesday.

"We believe that the government is required, in good faith, to consider the recommendations of the tribunal."

The Maori Party strongly opposes the sale of 49 per cent of the shares in Mighty River Power, Genesis Energy, Meridian Energy and coal miner Solid Energy.

Its MPs voted against the bill that gave the government authority to sell the shares, reducing it to a single vote majority.

The Green Party also says Mr Key was wrong to comment on the tribunal's hearing ahead of it announcing a decision, which is expected in about four weeks.

The Maori Council says it's confident the tribunal will rule in its favour, and it will use that to seek a High Court injunction to delay the share sales.

Mighty River Power shares are due to be floated late next month or in September.