UPDATED 8.51pm: NZ First leader Winston Peters has pushed out his deadline for announcing a coalition agreement to form the next New Zealand government - he now says it will be "as soon as possible" after Thursday.

Mr Peters, who will decide whether National or Labour leads the next government, had previously set Thursday as the deadline.

But after completing another round of talks on Tuesday night, he told reporters the target was to complete the negotiations by Thursday night.

He said he would not be making the announcement on Thursday night.

It would be made "as soon as possible after Thursday night" but he wouldn't go as far as to confirm the public would know his decision by Friday.

Meanwhile, the third day of talks closed with the Greens still shut out of the negotiations.

Mr Peters says he'll negotiate only with National and Labour, and seems to consider the Greens to be a left-wing faction of the Labour Party.

Greens leader James Shaw says he expects to sit at the table at some point, but Mr Peters isn't responding to that.

The Greens are a vital part of a centre-left deal because Labour and NZ First can't command a majority in parliament without them.

And the NZ First leader has acknowledged that whatever decision he makes, it won't please everyone.

"We are all sworn to secrecy to ensure we have frank and open discussions," he said in a Facebook post on Tuesday.

"You will all know, as well as us, that whatever decision we make it will cause disappointment and anguish - that's reality and there is no escaping that."

Specific policy points have been on the table during the third day of negotiations between NZ First and the main parties but they're keeping strictly to confidentiality agreements.

Cabinet minister Steven Joyce gave the thumbs-up as he left National's first session, while Labour leader Jacinda Ardern indicated after her morning meeting that social and economic progress were the focus.

"Our meetings have focused on our shared ideas, areas where we want to make sure that we progress New Zealand socially and economically, and that's where our focus continues to be," she said.

Mr Peters described the meetings as "very good".