Since the February earthquake 4200 Christchurch people have left not just the city but the country, 1700 more than the same period last year, while 1800 people arrived from overseas to settle in Christchurch, 800 fewer than the same period last year.
But the biggest change is a resurgence in migration to Australia - a net outflow of 3200 last month, 3100 of them New Zealand citizens.
In the year to July a net 32,600 people left for Australia, up from 16,500 the previous year and a 10-year average of 21,000.
But ASB economist Jane Turner expects outflows to Australia to peak in the coming months.
"Australia's labour market has slowed considerably over recent months. Meanwhile, economic pros-pects in New Zealand have improved, job growth now showing a firm recovery, which should convince some [Kiwis] to stay put - at least while the Rugby World Cup is on."
The migration outflow reduced inflation pressures by reducing demand for goods and services and relieving some of the stress on a tight housing market, Turner said.
BNZ chief economist Tony Alexander said changes in population growth tended to lag behind changes in economic growth. "That suggests a lift in population growth is likely from early next year."
Alexander expects the outflow of people to reverse in 2012 as labour and housing markets weaken in Australia but strengthen here.