Two former MPs are picking Labour as New Zealand First's more likely coalition partner, ahead of Winston Peter's announcement this afternoon.
But one - former National MP Paul East - said no matter who New Zealand First went with, it would end up being a one-term government.
"It'll be fractious and it won't last."
After an all-day caucus meeting at Parliament yesterday, Mr Peters said his party would be in a position to make an announcement this afternoon on the result of the post-election coalition negotiations.
He had advised the leaders of National and Labour of the timing of the announcement, he said.
Mr East - who flatted with Mr Peters in the 1980s when they were MPs together - said his heart wanted New Zealand First to pick National, "but my head says he'll go with Labour".
"[Mr Peters] would be absorbed too much by National, I think."
Picking a Labour coalition would annoy New Zealand First's membership, Mr East said.
"Most of them are former National members."
Former New Zealand First MP Pita Paraone said policy aside, Mr Peters' decision would come down to personality "and a question of trust".
But he too believed Mr Peters could be looking to Labour.
"If he was to note that the majority of New Zealanders or voters voted against the status quo ... [that] suggests to me that there was a wind or a desire for change," he said.
"If that was heeded by New Zealand First then obviously they would go with Labour."
Last night, National Party leader Bill English said his party's caucus and board would be briefed this morning on the negotiations to date.
He said they did not yet have a final deal with New Zealand First that was ready to ratify and there could be further negotiations with New Zealand First this morning.
"We have no indication from Mr Peters about what he's announcing," Mr English said.
It's understood Labour is in a similar position and its executive council has not yet been convened to sign off any potential final deal with New Zealand First.