WELLINGTON (AFP) - The leader of New Zealand's main opposition Labour Party quit on Tuesday (Aug 1) just weeks before a general election, citing "disappointing" opinion polls.

Outgoing Andrew Little said the centre-left party needed a fresh team at the top for the September 23 election after its support plunged to 20-year-lows of between 23 and 24 per cent.

"Recent poll results have been disappointing. As leader, I must take responsibility for these results," he said.

"I do take responsibility and believe that Labour must have an opportunity to perform better under new leadership through to the election."

Little stepped down immediately, with the Labour caucus set to elect a replacement later Tuesday. He backed his deputy Jacinda Ardern for the role.

The centre-right National Party-led coalition under Prime Minister Bill English is seeking a fourth term in the election and comfortably leads in the polls.