NZ First leader Winston Peters says he is "calling out" the Greens and warning of "consequences", after its co-leader Metiria Turei referred to his immigration stance as "racist".

The Greens and NZ First have a tense relationship, with both eyeing a deal with Labour after the election but the Greens fearing NZ First will try to lock them from gaining Cabinet seats as it has in the past.

Turei said on Sunday's Q and A programme that her party's relationship with Peters was "fine" and noted Peters had not ruled the Greens out, as he had in previous elections.

She said the Greens had not ruled him and NZ First out either, "because actually they may be necessary for the formation of a progressive government".

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But while ruling out supporting a National Government, she said the Greens could work with NZ First "if we have to for a progressive government" but she pleaded for voters not to make that necessary.

DAVID WHITE/STUFF The Greens and NZ First have a tense relationship.

And she implied that would not be blank cheque of support for a Labour-NZ First Government.

"But any government that we support or are part of has to be genuinely progressive. We are not going to accept an inferior deal."

However, she did rule out working with the National Party to form a government.

But it was her comments about Peters' immigration policy that saw him bite back.

Turei said he was "on a roll at the moment, which is I think a very racist approach to immigration, for example. The worst of his rhetoric is coming out."

In reply, Peters said he had a warning for the Greens: "Don't call NZ First racist - an allegation that is spurious - and think there won't be consequences."

He said the Greens, who launch their policy on water in Nelson today, believe Maori own the water.

"And like the Maori Party and the National Party that view is precisely what they are writing into law," he said.

"[Turei] then went on to say that she could work with NZ First as though we're going to accept an allegation that we are racist, when it is parties like the Greens that would take this country down the pathway to racial separatism. Racially separatist policies are deeply entrenched in the Greens policies."

"We are calling out the Greens right now," he said.

"Why should anyone believe the Greens are concerned about water, when they have such a racially jingoistic attitude towards its ownership."