As Prince William prepares to leave New Zealand, a poll of the Herald reader panel shows the 27-year-old in a neck-and-neck race with his father as the popular choice to succeed the Queen.

The survey - taken before the Prince's three-day tour - found 33.3 per cent wanted Prince Charles to be the next monarch, with 30.2 per cent favouring William. But 29.4 per cent of respondents preferred a republic in the event Queen Elizabeth II died or abdicated.

Women aged 18 to 44 and men aged 18 to 29 would prefer Prince William as the next head of state, while men aged 45 to 59 were particularly keen on New Zealand becoming a republic.

Almost half of the supporters of a republic - 49.1 per cent - had no opinion on who should be the first head of state. Former Governor-General Dame Silvia Cartwright was the top choice, with 15.5 per cent backing.

Monarchy New Zealand spokesman Simon O'Connor said the results illustrated the problem of trying to choose a head of state, while reinforcing the overwhelming support for the monarchy.

Lewis Holden, chairman of the Republican Movement of Aotearoa New Zealand, said the results were what he expected and the numbers of people supporting a republic were in line with other surveys.

The online survey of the Herald Readers' Panel was conducted by the Nielsen Company between December 10 and 17.

When Queen Elizabeth II dies or abdicates, who should replace her as New Zealand's head of state?

Prince Charles - 33.3 per cent
Prince William - 30.2 per cent
Another royal - 1 per cent
NZ to be a republic - 29.4 per cent
No opinion - 6 per cent

If New Zealand became an independent republic, who should be the first head of state?

No opinion - 49.1 per cent
Dame Silvia Cartwright - 15.5 per cent
Sir Paul Reeves - 11.7 per cent
Jim Bolger - 3 per cent
Jonah Lomu - 1 per cent