The net flow of migrants turned sharply negative again last month, dragging the annual gain down to just 770, its weakest for 10 years.
September's seasonally adjusted net outflow of 660, after a gain of 120 in August, means the flow of permanent and long-term migrants has been negative for six of the seven months since the February earthquake.
"Six hundred Christchurch residents moved overseas in September 2011, up from 400 in September 2010," Statistics New Zealand said.
"Since the devastating earthquake on February 22, there have been 5500 departures from Christchurch compared with 3300 in the same period in 2010."
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Goldman Sachs economist Philip Borkin said given ongoing aftershocks, rebuilding delays and insurance uncertainties, the ouflow from Canterbury might continue.
But it explains only a fraction of the drop in the annual inflow of migrants; the net gain of 770 in the past year is just under half the 13,900 gain the year before, and well below the average gain of 12,000 over the past 20 years.
In the year to September, 48,800 people left for Australia (90 per cent of them Kiwis), offset by 14,700 coming the other way (63 per cent of them returning New Zealanders).
There was a net gain of 5700 from the United Kingdom, 5400 from India and 4600 from China.
ASB economist Jane Turner expects permanent departures to Australia to ease in coming months as employment growth there slows, while the labour market in New Zealand gradually recovers and skill shortages emerge, encouraging a pick-up in inward migration.
In the meantime, the weakness in net migration highlighted ongoing weakness in consumer demand and the lack of any urgency for the Reserve Bank to raise the official cash rate, she said.