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Statistics New Zealand figures showed the seasonally adjusted permanent long-term arrivals from Australia in June matched the number of departures (2000), resulting in net transtasman migration of zero.
ASB economist Chris Tennent-Brown said August 1991 was the last time a net migration loss to Australia was not recorded.
''Over the full year to June 2014, New Zealand still had a net loss of 8300 migrants to Australia but that is significantly down from 31,200 in the year to June 2013.''
Other milestones included permanent and long-term migrant (PLT) numbers of 4270 for the June month being the second best on record. The highest on record of 4700 came in February 2003.
The net PLT migrant gain reflected arrivals of 9210 (up 1.2% in the month and 12.5% for the year) and departures of 4940 (down 3.5% in the month and 17.8% for the year).
In the June year, permanent and long-term arrivals were 100,800, up 14% from 2013 and the first time more than 100,000 PLT arrivals had been recorded in a year, according to Statistics NZ.
In contrast, annual departures in the year were 62,466, the lowest number of annual departures for 10 years.
Mr Tennent-Brown said relative market performance was the key driver of transtasman migration.
''Given Australian labour market indicators have improved over recent months, we do not expect to see a slowdown in New Zealand's net migration inflows over the rest of the year. We expect annual net migration will peak around 42,500.
"But at the moment, the risk to this forecast is to the upside.''
In the past quarter, the level of net migration arrivals annualised closer to 50,000, he said.
The Reserve Bank was very focused on the demand side of the migration, going as far as suggesting a scenario in which much stronger than expected migration resulted in higher interest rates.
The other side was the effect on the labour market, where migrants added to the pool of workers available to work and in doing so, kept a lid on inflation pressures, he said.
Westpac senior economist Felix Dulbruck said net migration was running ahead of the Reserve Bank's forecasts in the June Monetary Policy Statement, the single bright spot in what had been a disappointing run of New Zealand data for the central bank.
Seasonally short-term arrivals and departures both fell in the month.
''We were slightly surprised by the sharp drop in New Zealand short-term departures, given still relatively high consumer confidence and the continued drawcards of a high New zealand dollar and cheap overseas travel.''