Labour's poll support has slipped after an initial surge following David Cunliffe's election as leader, the latest Herald-DigiPoll survey shows.
The Maori Party would hold the balance of power if the figures were translated to an election result.
With the left and right blocs fairly evenly split, it could be a close election next year.
Neither National nor Labour would be able to form a government without the Maori Party.
Labour has fallen 2.3 points in the survey to 35.4 per cent. In the September poll, it had a surge in support and could have formed a government with just the Greens and Mana.
National has risen 3.1 points and Prime Minister John Key has somewhat recovered in the preferred Prime Minister stakes, after taking a 9.4 point dive in the last poll.
He has jumped 6.1 points to 61.9 per cent, well ahead of Mr Cunliffe on 16.5 per cent.
Mr Key told the Herald last night that it was good to end the year in a strong position. "That reflects the growing economic confidence and the acknowledgement by voters that we've steered the ship on a very deliberate and accurate course to economic prosperity."
He said that strong year-end polls were important to parties "because people go on their summer holidays and over the barbecue they talk about who is likely to win the election and this poll has got to be very good news for National".
Mr Cunliffe was elected in September after the resignation of David Shearer in August.
Mr Shearer's personal popularity in a Herald-DigiPoll survey peaked in March this year when he was preferred by 18.5 per cent, which Mr Cunliffe has yet to surpass, and the party vote at the time of 36.4 per cent was close to its current polling.
The Maori Party would hold the balance of power under this poll, assuming it returned three MPs, but two of its current MPs, co-leader Tariana Turia and Maori Affairs Minister Pita Sharples, are retiring next election.
The poll shows Act and United Future as having virtually no party vote support. The seat calculations here assume the retention of currently held constituency seats for Mana, the Maori Party, Act and United Future, as is the case with most polls under the two-vote MMP system.
But in this particular poll, National could form a government with the Maori Party alone, without an Act or United Future add-on.
Labour would be able to form a government but it would need three other support parties: the Greens, Mana and the Maori Party.
The poll of 750 was conducted December 9-17 and the margin of error is 3.6 per cent. The party vote results are of decided voters. Undecided respondents were 12.6 per cent.
• National - 46.8% (+3.1%)
• Labour - 35.4% (-2.3%)
• Greens - 10.8% (-0.5%)
• NZ First - 3.9% (-0.5%)
• Maori Party - 1.3% (+0.5%)
• Mana - 0.9% (+0.2%)
• Act - 0% (-0.1%)
• United Future - 0% (Same)
• Conservatives - 0.7% (-0.3%)
• Legalise Cannabis - 0.1% (Same)
Preferred Prime Minister
• John Key - 61.9% (+6.1%)
• David Cunliffe - 16.5% (-0.3%)
• Winston Peters - 7.3% (+1.1%)
• Russel Norman - 3.4% (-0.3%)
• Helen Clark - 3.2% (-0.3%)
Seats in the House
(Assumes Maori Party, Mana, Act and United Future retain electorate seats)
• National - 59
• Labour - 44
• Greens - 14
• Maori Party - 3
• Mana - 1
• Act - 1
• United Future - 1
- Source: Herald-DigiPoll survey of 750 people, Dec 9-17. Margin of error 3.6%.