The republic debate's started up again in New Zealand.

Labour leader Jacinda Ardern has raised the prospect of ditching the monarchy, saying she's disappointed the conversation wasn't had at the same time as the flag debate.

Republic NZ's Lewis Holden told Mike Hosking polls indicate up to half the population backs the move.

"The actual changes themselves aren't very complicated because we effectively have a full head of state in the governor general, so it's really about making that position our head of state."

But Monarchy NZ's Josh Chandulal-Mackay said a new president would need to be elected.

"So in an election they need to appeal to the electorate for the support and actually create this huge amount of division that I don't think needs to be a part of what the head of state represents which is the entire country."

LISTEN ABOVE AS LEWIS HOLDEN AND JOSH CHANDULAL_MACKAY SPEAK WITH MIKE HOSKING