Prime Minister John Key said he believes there is a growing momentum toward agreement on a Trans Pacific Partnership deal this week as leaders hold sideline discussions in New York.

Mr Key spent his first evening in New York at a reception hosted by Japan's Prime Minister Shinzo Abe for a small group of leaders and discussed TPP negotiations with him. He also hoped to talk to US President Barack Obama about it during a leaders' lunch early tomorrow morning NZ time.

The leaders' week at the UN coincides with officials meeting in Atlanta to try to resolve the remaining barriers to an agreement, which include access for dairy.

Trade Minister Tim Groser previously said it was uncertain if he would go to Atlanta.

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Today Mr Key said it was now "highly likely" Mr Groser would attend - a sign that an agreement could be imminent but Mr Key said a bit more movement on dairy was needed.

"I always said it would take one last shove by leaders to get that over the line. I think there is some growing momentum now around potentially a deal emerging from Atlanta later in the week."

He said it was not a guarantee and would not confirm reports in Canadian and US papers that the two countries were about to budge on allowing more favourable dairy access.

He said the current position was not acceptable to New Zealand.

However, both Abe and Obama knew how important dairy was for New Zealand and that it needed some movement on access.

"There's an lot of discussions and quite a lot of communications between leaders. This thing needs one last shove. They know there's only a limited window of opportunity to get this deal over the line and I think they are going to put a lot of effort while we are all here together to see if we can't get some meaningful progress there."

He said Obama had made his views clear. "We have had a lot of conversations over a long period of time about TPP. He's left me under no doubt about his determination and commitment to see TPP concluded. He can also see the window of opportunity closing in on us."

He said there was a lot riding on it for New Zealand because the US was such a big market. "So there's a lot at stake for New Zealand and I think there's potential for a very good deal."