Massey University sociologist Paul Spoonley said the figures showed Australian migration was "a North Island phenomenon".
"And really, it's the top half of the North Island which is losing the numbers ... Almost without exception, the top group is north of Taupo."
That was to be expected because that was where the bulk of the country's population lived, and centres there were continually growing, Professor Spoonley said.
"There's a strong demographic factor in all of this - the most populated parts of New Zealand are providing the largest groups leaving."
The main cities in the South Island were not growing at the same rate, so the turnover of people was not as large.
There were a few exceptions: the number of people leaving Kaikoura more than doubled in three years and the number quitting Gore almost tripled.
Between April 2009 and last March, the number of people moving from Auckland to Australia long term or permanently rose 36 per cent.
The increase for Hamilton was 63 per cent and for Christchurch 55 per cent. "With Christchurch, you've got the combination of it being New Zealand's second largest city but then of course there's been the earthquake effect too," Professor Spoonley said.
People from Whangarei, Auckland, Hamilton, Tauranga, Wellington and Christchurch made up 60 per cent of those migrating to Australia.
Tauranga - where the migration to Australia took 13.75 people in each thousand of population in the year to last March - was one of the most interesting regions, as it was an area people flocked to for the lifestyle, Professor Spoonley said.
Tauranga Mayor Stuart Crosby believes people are leaving because the construction industry has slowed significantly over the past three or four years.
"It's a pretty safe assumption that it's a large number of our tradespeople leaving," Mr Crosby said.
That was a concern, because construction was starting to pick up again and there might not be enough skilled workers left.
But Mayor Crosby believed many of those who had moved to Australia were planning to come back once they were financially secure.
"I've got two nephews working in Australia, in the trades ... They want to make good money before they come home, but they will come home," the Tauranga leader said.
In the year to March, Kaikoura lost 1.4 per cent of its population, the highest proportion in the country.
Mayor Winston Gray also believed it was young tradespeople who were leaving, and echoed Mr Crosby's belief that they would return.
"They're almost all quite young, single ... and say, 'Right, we'll go off to make some money', then eventually come back here after they get themselves into a strong financial position."
There was also a small number of people in Kaikoura who commuted to Australia to work for up to six weeks at a time before coming home to their families for a while.
Mr Gray said most of the people leaving Kaikoura were going to Western Australia.
Professor Spoonley said there was likely to soon be "a big bite taken out of the age cohorts", as school leavers and graduates were the groups who had the most difficulty finding work in New Zealand and were the ones leading the charge to Australia.
Companies had also been recruiting New Zealanders.
Among them was Reciprocus, from Perth, which held seminars in Upper North Island small towns recruiting people to work in mines in Western Australia.
As well, Professor Spoonley said, people in New Zealand were staying in their jobs, reducing opportunities for others to get employed.
"So there's a strong push factor of not enough good-quality jobs that are paying well here, and the pull factor that those jobs are available in Australia."
The departure figures were for New Zealand citizens only. Statistics NZ demography spokesman Nicholas Thomson said it was important to note the population of the districts included people who were not citizens.
"That would affect somewhere like Auckland more, though, because Auckland does tend to get a lot of new immigrants and has a lot of non-New Zealand citizens," Mr Thomson said.
As well, the 2012 departure data was compared to population statistics from June 2011.
But that was not a great limitation because population figures did not change much between years.
School loses 13 % of its students across the Ditch
Last year, Wesley Intermediate School in Auckland lost 18 pupils - 13 per cent of its roll - because their families moved to Australia.
The principal of the Mt Roskill school, Nigel Davis, said most of those who moved went to Perth, a few to Melbourne and others to the Gold Coast.
Ninety per cent of the families migrated because the parents could not get work: "They told us they couldn't get jobs in New Zealand so were going to try in Australia."
The intermediate had between 130 and 140 pupils on its roll - "depending on which month it is and how many kids left for Australia", Mr Davis said.
Last year, the loss of students to Australia was balanced by the number of children arriving from other areas, including a "fair few" who moved up from Christchurch.
However, all but one of the Christchurch students moved to Australia.
"Luckily our roll remained stable," Mr Davis said. "But we were stunned about how many people were moving to Australia. You hear it reported, but when you see it in reality, it's really something else."
He said the migration to Australia was hard on both the child who was leaving and the teacher whose class the pupil was in.
Eight years ago, a study found that Wesley Intermediate was the only school that did not have a problem with transient students and kept a stable roll.
"But last year was totally different for us," Mr David said. "It was quite remarkable. It could be that it's one of the pockets in Auckland which has that very high percentage of people leaving for Australia."
