WELLINGTON (AFP) - Populist lawmaker Winston Peters is set to pick a winner in New Zealand's deadlocked general election this week after again finding himself cast as kingmaker thanks to the country's quirky electoral system.

It is the third time since New Zealand adopted the mixed member proportional (MMP) voting system in 1996 that an election has hinged upon the whim of the 72-year-old maverick.

At the most recent poll on Sept 23, neither of the major parties - National and Labour - won the 61 seats needed for victory even with the help of political allies.

It means they both require a coalition with Peters to gain the outright majority needed to form a government under the MMP system.

True to form, Peters has given no indication of whether he prefers conservative Prime Minister Bill English's National Party or opposition leader Jacinda Ardern's centre-left Labour.

He has a self-imposed deadline of Thursday (Oct 12) to decide, although there is no guarantee he will stick to it.

The unpredictable powerbroker has backed both parties in the past and is in a position to drive a hard bargain in return for his support.

"I'm a very reasonable person but I don't sell myself or my principles out," he said before the election.

Tail wags dog

The sight of English and Ardern, who between them won 81 per cent of the vote, scrambling to woo Peters, who attracted just seven percent, has rankled some.

"Winston Peters, with seven percent of support, has 100 per cent of the power to anoint the next prime minister," an editorial in leading current affairs magazine "The Listener" said.

"For a country that values fairness, that feels intuitively wrong." Another criticism has been that voters who chose parties based on their campaign platforms now have no idea what policies will emerge from the backroom talks.

While best known as an anti-immigration campaigner, Peters has a grab-bag of other pet policies he has described as "bottom-lines" for his support.

They range from revamping the central bank and slashing migrant numbers to more offbeat demands such as showing All Black Tests on free-to-air television and ensuring government offices use carpets made of New Zealand wool.

Some, such as axing parliamentary seats reserved for indigenous Maori, have been jettisoned but there is uncertainty about the issues on which Peters is prepared to dig in his heels.

A further complicating factor is Peters' notoriously thin skin and ability to hold a grudge.

He insisted before the election that personal bias would have no role in coalition negotiations, only to issue a bizarre warning to English and Ardern last week.

"Don't send along the wrong people (to coalition talks)... if you were in a commercial or another setting, you'd be very careful as to who you sent," he said.

"You wouldn't want somebody's past behaviour and obnoxiousness to be a part of the problem, would you?"

'We can't win'

It means slights and gripes involving Peters, some dating back decades, have come under scrutiny in case they sway the thinking of the grumpy septuagenarian.

Pundits with long memories pointed out that English seconded a motion to expel Peters from the National Party in 1992 and the pair have never been close.

On the other side of the political fence, the Greens angered Peters this year when they labelled his fiery anti-immigration rhetoric racist, prompting him to warn at the time there would be consequences.

Peters once famously said he "did not care about the baubles of office", but his track record suggests otherwise.

He supported National in 1996 in return for being made deputy prime minister and Labour in 2005 when it gave him the plum job of foreign minister.

Peters said he would face criticism regardless of who he supports.

"The whole thing has been depicted as one man holding the country to ransom," he told reporters, defending his democratic credentials.

He added: "We just can't win. You can't win with the public, you can't win with the media, you can't win with the commentariat."