Emigrants outnumbered immigrants by 100 in the year ended October, the first annual net outflow for 10 years.
There was a net outflow of 650 permanent and long-term migrants, seasonally adjusted, last month.
For seven of the eight months since the February earthquake in Christchurch the net flow has been negative.
Since the earthquake 6000 Christchurch people have left not just the city but the country, 2300 more than in the same period last year, while the inflow of migrants to Christchurch at 3200 is down 1100.
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"Given the continued delays with reconstruction, insurance market gridlocks and ongoing aftershocks, it is quite likely that this theme continues," Goldman Sachs economist Philip Borkin said.
"But once it is clear that earthquake reconstruction will begin, the trend in Canterbury will reverse as resources are drawn to the region."
Total departures last month were down 290 from September, seasonally adjusted, a drop entirely explained by fewer people heading to Australia, Infometrics economist Gareth Kiernan said.
"This easing in the number of people heading across the Tasman may be reflective of a softening of the labour market in Australia, where the unemployment rate has edged up from 4.9 per cent to 5.2 per cent since April," he said.
"Although departure numbers are likely to continue pulling back due to the weaker Australian economy, it is likely to be the first quarter of 2012 before the annual net flow bottoms out at around minus 2500."
Statistics New Zealand said 49,000 people left for Australia in the past year, offset by 14,500 in the other direction. In both cases most migrants were New Zealand citizens.