A Labour-Greens coalition is most likely to come out on top at the next election, according to a new poll.

The latest poll from Roy Morgan shows a potential Labour - Greens alliance, while down three percentage points, could still govern with 46.5 per cent support.

Labour polled 35.5 per cent support on its own, down 1.5 per cent, while the Greens slid 1.5 to 11 per cent.

The National Party alone polled 42 per cent support, which was up 0.5 of a percentage point on Roy Morgan's last poll. Its coalition partners also saw a slight rise - ACT up 0.5 of a point to one per cent, United Future rating at 0.5 per cent and the Maori Party unchanged on 1.5 per cent.

Gary Morgan said the poll showed a potential Labour - Greens Alliance was in a strong position to win Government in a year's time with the support of New Zealand First (4.5 per cent, down 0.5 per cent).

"National have work to do to retain Government although Prime Minister John Key has this week suggested the Conservative Party (2.5 per cent, up 2 per cent) could be a possible Coalition partner for National in a future Government."

The figures however, are in contrast to two major polls carried out earlier in the week - both showing National still had the ability to win next year's election.

The Fairfax Media-Ipsos poll showed that a narrowing gap between the two big parties, in the wake of the Labour leadership ''primary'', had reversed leaving National on track to win the next election.

In that poll Labour was up two percentage points to 33.6 per cent since the last Fairfax poll, completed in August before the leadership spill that saw David Cunliffe replace David Shearer.

National was also up two points and held a huge 17 point lead over Labour, winning the backing of more than 50 per cent of committed voters.

Labour's main ally the Greens retained a solid block of support at 10.7 per cent however, and National's allies ACT and United Future barely registered and the Maori Party was polling at just 0.7 per cent, the same as its rival Mana.

A TVNZ Colmar Brunton Poll also showed support for Labour had stalled.

Although that poll had National slipping two points to 45 - narrowing the gap between the two main parties to 11, while Labour remained steady on 35 per cent.

Gains made by the Greens however - climbing a point to 13 per cent support - put the Labour Party in close contention for being able to form a Government next year provided the Mana Party retained its seat.

The Roy Morgan poll surveyed 847 electors from October 14-27.

Both the Fairfax and TVNZ polls surveyed just over 1000 voters and had margins of error of plus or minus 3.1 per cent.