NZ First MP Fletcher Tabuteau says the party is "getting close" to a decision.
Kingmaker Winston Peters held secret meetings with National leader Bill English and Labour's Jacinda Ardern on Tuesday night, meaning an announcement on the next government isn't far away.
On Wednesday morning, Mr Tabuteau gave a long pause before announcing " I don't know" with a wry smile when asked if a decision was likely later in the day.
He was heading into the party's 9am caucus meeting. Mr Peters was understood to have already gone into the meeting through a side entrance.
Mr Peters met the party leaders separately in the Beehive following two days of discussions by NZ First's caucus and board about the policy concessions offered by the main parties in return for its support in forming a government.
Mr Peters spoke to media after the caucus and board discussions but made no mention of Tuesday night's meetings.
Each of the talks lasted about half an hour and raised speculation Mr Peters had given them a heads-up on an imminent announcement about which side NZ First would back.
But he could have been updating them on progress made by NZ First's discussions and laying the groundwork for further top-level talks.
He had earlier told media there was still some serious talking to be done before NZ First made its decision.
"When we think we've got the policy wrapped up, every loose end wrapped up, we'll talk to both sides about what it is they want," Mr Peters said.
That was taken as meaning there would be more negotiating sessions involving NZ First and teams led by Mr English and Ms Ardern.
Mr Peters had earlier confirmed that neither ministerial positions for NZ First's MPs nor the form of the next government had been discussed.