Support for the ruling National Party has fallen to its lowest level since the 2011 election, and a potential Greens/Labour coalition is now polling higher.
National was at 44 percent support in a Roy Morgan Poll taken between July 23 and August 5, down 3.5 percent from the last poll taken between July 9 and 22.
Support for Labour rose 2 percent to 32 percent, while backing for the Greens rose 3 percent to 14 percent.
National's result is at its lowest level since the election and the 12 percent lead over Labour is the closest gap between the two main parties since just after National won Government in 2008.
If an election were held now it would be too close to call and depend on the voting results of minor parties and whether they crossed the 5 percent threshold to win list seats.
Support for National's coalition partners was little changed with the Maori Party on 2 percent, ACT on 0.5 percent and United Future on 0.5 percent.
Support for the Conservative Party, which has taken a strong position against law reform to allow gay marriage, has fallen 1.5 percent to 1.5 percent.
New Zealand First had 4 percent support, and the Mana Party 1 percent.
NZN