New Zealand's populist kingmaker Winston Peters says he will finally reveal on Thursday who he is supporting in the country's deadlocked general election, after keeping voters waiting almost four weeks.

The South Pacific nation has been in political limbo since the September 23 vote failed to deliver a clear majority for either conservative Prime Minister Bill English or his centre-left rival Jacinda Ardern. 

They both require support from Peters' New Zealand First (NZF) to pass the 61 seats needed for a win, giving it a decisive role in the election even though it only won seven percent of the vote.

The 72-year-old political veteran has already missed several self-imposed deadlines to settle the issue but indicated in a statement Wednesday that he was at last ready to show his hand.

"New Zealand First will be in a position tomorrow (Thursday) afternoon to make an announcement on the result of negotiations following the 2017 general election," he said.

Peters has thrashed out policy positions over 11 days of negotiations with Labour, National and his own NZF, including one-on-one meetings with English and Ardern.

The talks have been held in secret but Peters' demands are expected to centre on issues such as cutting immigration, banning foreign home buyers and boosting regional development.

Just as important could be what ministerial position NZF's potential coalition partners are willing to offer to Peters.

In the past, he has claimed to scorn "the baubles of office" but his record shows he will support either side of politics if the right offer is made. 

He opted for National in 1996 in return for being made deputy prime minister and backed Labour in 2005 after it agreed to make him foreign minister. 

But he did not see out either term of office as a minister, leading critics to say that any government that relies on Peters to prop it up is inherently unstable. 

"I'm thinking it won't last whatever it is... there's an inbuilt self-destruct mechanism," former MP Peter Dunne said this week. 

"The fact that you'd build something on the basis of vanity suggests there's going to be a point where the vanity's upset." 

Peters was sacked as deputy prime minister in 1996 in a row over privatising state assets and stood down as foreign minister in 2008 amid an investigation into undeclared political donations.