New Zealand's economic miracle - the desire of people to come and live here - show's signs it has peaked, according to latest data from Statistics NZ.

The pace of net migration was almost unchanged from April and technically takes annual migration to a new record high at 68,432 arrivals for the 12 month period.

But the monthly numbers have now declined four times in a row. That's a concern because strong population growth has been effectively buffering the economy from the shock of the dairy downturn.

Seasonally adjusted figures for May showed a net gain (more arrivals than departures) of 5,500 migrants in May 2016. Since reaching a peak of 6,200 in November 2015, the seasonally adjusted net gain in migrants has averaged 5,700 a month.

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Much of the migration gain has come from a reversal of the historically more normal trend of kiwis departing for Australia.

"Returning New Zealanders and Australians remain the two main sources of arrivals, with many of the former coming back from Australia, ASB economist note.

"However, the Australian labour market has been showing signs of recovering, in contrast to NZ's which has slowed after a period of very strong growth.

"The inflow from Australia could be additionally dampened if new Australian citizenship policies encourage more New Zealanders to stay in Australia for longer, in order to gain citizenship."

Westpac economists say today's data provides "further confirmation" that this cycle of migration has peaked.

"We expect annual net migration to fall rapidly over the coming year or two, as foreigners who arrived on temporary work or student visas over the past three years begin to depart, and as the recovering Australian labour market begins to attract New Zealanders across the Tasman," Westpac says. "However, even if net migration drops away from its peak, it will still be very high by historical standards for some time."

Despite annual GDP growth coming in at a relatively healthy 2.4 per cent for the year to March, economist have noted that is underpinned by New Zealand's growing population.

When population growth is factored in GDP per capita growth increased at just 0.1 per cent in the first quarter of the year. On that basis annual GDP growth per capita would be less than half a per cent.

Migration doesn't look likely to fall off a cliff but if the trend continues then we will need other parts of the economy to fire up to avoid a significant slowdown.

While construction is Auckland is expected to keep picking up, the Christchurch rebuild will be winding down. Westpac's Dominick Stephens has argued for some time that this creates a risk that Treasury's economic forecasts are too rosy.

Meanwhile Tourism held firm with short term arrivals up 0.1 per cent taking year on year growth for the booming sector to 10.5 per cent year on year.

The sector - along with some resilient agricultural exports like kiwifruit, apples and meat - have added to the strength of the economy.

Here's hoping that continues to hold firm and net migration declines at a moderate pace, slow enough to buy time for the dairy sector to rebound.