New Zealand First leader Winston Peters says the major party campaign launches at the weekend looked like "a couple of damp squibs," and suggestions against strategic voting are "very, very ill-informed".

Peters told RNZ that National's launch was "seriously lacking in energy", while Labour's seemed to be a convention of expletives, "which I was absolutely astonished at".

A fiery Labour leader Chris Hipkins swore while denouncing National leader Christopher Luxon’s comments on Labour’s tax policies as “lies” and “bullshit”.

Peters believed Labour’s launch was "manufactured" and manipulated for the media - "and the media went along with it".

On Hipkins' performance, Peters said he had never seen a Labour leader sink to that level of language.

"There's no reason for standards to be sacrificed in pursuit of politics."

Peters also said of National's launch that it was "rather desperate" to have a former prime minister on stage with nobody behind him "giving out the wrong message".

Sir John Key warned against strategic voting in his speech, saying voters shouldn't try do something "you think is clever" that is the "opposite of clever".

It referenced a suggestion voters on the right give their party vote to a minor party, and electorate vote to the National candidate, with the intention of creating an overhang.

Peters said it was the wrong message because the "very manipulation of the electoral system” Te Pāti Māori and those on the left were engaging in "has to have a response".

"The response that Mr Key set out was simply just not appropriate and not right, and was very, very ill-informed in my view.

"For all things, and with every action, there's gotta be a reaction. You cannot just fail to respond. That's what an election campaign's about."

Asked about comments by Luxon on RNZ's Morning Report programme on Monday suggesting that NZ First’s policy to buy back the BNZ was "madness", Peters said it was "extraordinary" and showed a "terrible ignorance of history".

Peters suggested Luxon find out more about these matters before he "expresses an opinion".

He described the BNZ as a product of Labour and National working together a long time ago to take on the foreign banks and get fairer costs and outcomes for New Zealanders, before they decided to privatise it.

"So why would we sacrifice that when Singapore and every other smart economy has got their own banks, excepting the prime minister for reasons best known to himself, thinks that this is a bad idea."

Asked about National's attack on Labour as introducing multiple new taxes when including promises by its potential coalition partners the Greens, Te Pāti Māori and Opportunity, and whether National should be assessed in the same way according to its coalition partners, Peters said "of course we should be", but he emphasised buying back BNZ was not a cost.

He said it shouldn't be assessed in a first-past-the-post way, rather the option should be assessed as opposed to in relation to National.

"It's going to be a coalition government, and on that basis should be assessed, yes," but the difference was his policy would expand New Zealand's wealth, he added.

Asked if Luxon had cognitive dissonance on the issue, if not applying the same assessment as he does to Labour, Peters said "that's one way of putting it".

"The better way of putting it is: learn to read the room if you want to be in politics for any duration of time."