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."
Goldman Sachs economist Philip Borkin said given ongoing aftershocks, rebuilding delays and insurance uncertainties, the ouflow from Canterbury might continue.