The latest monthly Roy Morgan survey shows Labour has just 24 percent support, down two percent from last month.
The right bloc is cruising towards an election win courtesy of a big boost to Act.
While centre-right opposition National also fell, down 2.5 points to 31, a surge from David Seymour's libertarian party to 18 percent, up four, means they can govern in coalition.
The Australian company's result is marginally out of step with Kiwi pollsters, who have both Labour and National higher - but with a similar margin - and Act polling in the low teens.
However, the result is the same: an edge to the opposition parties of the right which would make National leader Chris Luxon prime minister.
The campaign proper began on the weekend with Labour and National holding their party launches in Auckland.
The poll results do not capture those events, when Labour launched a new policy to make free basic dental care to under 30s.
It also does not capture attack ads launched by the union movement targeting Mr Luxon, arguing the former executive is out of touch and the wrong choice during a cost of living crisis.
"I just think it's incredibly sad and pathetic, to be honest," Mr Luxon said.
Prime Minister Chris Hipkins responded by sharing examples of National ads attacking him released over the last year.
The pettiness is unlikely to endear either major party to Kiwis, and is perhaps why minor parties are closing in on a record share of the vote at a New Zealand election.
Winston Peters' populist New Zealand First party would win seats in parliament under the Roy Morgan results, polling 5.5 percent, while the Maori Party would also grow its share to four percent.
Labour's potential coalition partners the Greens also enjoyed a hefty bump, from 9 to 12.5 percent.
In good news for the left-wingers' hopes of growing their footprint on the electoral map, the Greens have slightly out-polled Labour in Wellington.
The Greens had 20.5 percent support in the capital, where they are eyeing the seats of Wellington Central and Rongotai, compared with Labour's 20 percent.
ROY MORGAN NEW ZEALAND AUGUST POLL
National - 31 percent (down 2.5)
Labour - 24 (down 2)
ACT - 18 (up 4)
Greens - 12.5 (up 3.5)
NZ First - 5.5 (up 0.5)
Maori - 4 (down 2)
TOP - 2 (down 2)
