Updated 12.45pm: New Zealand's current immigration boom isn't expected to last.

Migration and its impact on the economy is being discussed at the New New Zealand forum in Wellington this morning.

Westpac senior economist Felix Delbruck says the current peak in immigration is due to fewer kiwis leaving and more coming back from Australia.

He says struggles facing the Australian labour market will wash out, and New Zealanders will continue to head across the ditch.

Mr Delbruck says Auckland needs to grow into a city that can rival the likes of Melbourne and Sydney.

Experts are reiterating the need for New Zealand to look closely at its changing population.

Massey's Distinguished Professor Paul Spoonley says projections show regions in particular are set to be hit as the people in their late teens and 20s continue to head for the city.

He says in ten years time regional centres won't be growing at all, except in the over 65 population.