"Net losses have been recorded in 11 of the 12 months since the February 2011 earthquake in Christchurch," Statistics NZ said.
Kiwis have been quitting New Zealand to seek a better standard of living and higher wages across the ditch.
The National Party won office campaigning on a promise to stem the outflow but departure numbers continue to rise.
Immigration expert Paul Spoonley said the record outflow this February was "unexpected" because the number of people leaving quake-hit Canterbury was likely to be falling.
"This is jobs-driven migration to Australia, and what surprises me is that we have been told the Australian labour market is soft, and yet people are still going," said Professor Spoonley.
"The numbers going will come down right through this year, because the predictions are that the New Zealand labour market will slowly pick up."
Australia offers a higher average wage and longer paid parental leave.
Professor Spoonley, a sociologist at Massey University, said a second group of Kiwis - those leaving to join family who had moved across the ditch - also fuelled departure numbers.
The 2006 Census showed about 390,000 people born in New Zealand were living in Australia, but the numbers are expected to have increased significantly since.
Auckland was the only region to record a net gain of international migrants last month.
The net loss of migrants in the last year comes despite increases in the number of people moving here from Britain (up 5300), India (5000) and China (4800).
An extra 300 non-New Zealand citizens arrived on work visas last month. Immigration New Zealand is expecting demand for labour migration to increase alongside economic recovery, and the Canterbury rebuild could lead to a further increase of skilled migration numbers.
The number of tourists arriving in the year to February 29 was 259,100, down 3 per cent on the previous 12 months.
Fewer visitors arrived from Britain, Japan, Hong Kong and China, despite February having a 29th day this year. "The decrease was partly due to the Chinese New Year holiday period being in January in 2012 as opposed to February in 2011," said Population Statistics manager Andrea Blackburn.
Expat Kiwis making home visits drove an increase in visitor arrivals from Australia.
TRYING HIS LUCK IN LUCKY COUNTRY
Shane Ball is quitting New Zealand today to "live his dream" in the mining town of Kalgoorlie, Western Australia.
The 33-year-old former security guard is dreaming of owning his own home, and providing a better future for his children, aged 3, 8 and 12.
"I'm leaving because the economy here sucks ... I can't afford to buy a house here, or even have any savings, and I need to have a different lifestyle," he said.
"I've been working like a dog here and getting hold of that first home is still an impossible dream."
Auckland-born Mr Ball said he was following in the footsteps of his sister, who had gone to Australia before him and was now "far better off".
"I have seen how much my sister's kids have progressed in school too, and decided my kids deserved a better future too," he said.
Mr Ball does not have a job lined up but is confident of getting one, having worked as a mental health support worker in Sydney in 2005.
"Then I was working half the hours and earning twice as much."
Mr Ball, who was living in Manukau, said he chose Kalgoorlie because it had a "more relaxed pace" and "affordable housing".
He was also looking forward to the warmer Australian weather after New Zealand's "crap summer".
His wife, Kelly, and their children will join him by Christmas.
