Christchurch lost 4600 residents and the Canterbury region shed 1800 in the year to June 2012.
Statistics New Zealand’s latest estimates take account of the number of people who have left and those who have arrived.
In the four-year pre-earthquake period ended June 2010, the city's population grew at an average annual rate of 1%, with population gains from a natural increase – 2200 a year on average – and a net migration gain of 1600 annually on average.
The latest population decrease by 4600 (1.2%) in the June 2012 year was caused by a net migration loss of 6000, partly offset by a natural increase of 1400.
In the 2011 June year, Christchurch city's population dropped by 8900, or 2.4%, through a net migration loss of 10,600, partly offset by a natural increase of 1600. Over the two years ended June 2012, the city's population declined by 13,500 (3.6%) through a net migration loss of 16,600, partly offset by a natural increase of 3100.
Statistics NZ used international migration statistics, primary health organisation enrolments, employer data, school rolls and electoral enrolments to assemble the data.
These sources indicate that between June 2010 and June 2012 the population aged 0-19 years in Christchurch city decreased by 9300 (9.6%), while people aged 35-49 fell by 5700 (7%).
This indicates a net outflow of children and their parents over this period. A decrease of 2900 people aged 15-19 reflects fewer young adults moving to Christchurch to study, Statistics NZ says.
But the male population aged 20-34 increased by 500 over the two-year period, while the corresponding female population decreased by 1700, reflecting a net inflow of young male workers.
Over the two-year period, the population aged 50 years and over grew slightly, up 2700 (2.3%) because of people moving into this group from younger ages and indicating that people aged 50-plus were less likely to leave, Statistics NZ surmises.
At the same time, Auckland’s population rose by 21,700, with one in three Kiwis now living in the region.
The population of the North Island grew by 27,800 (0.8%) through a natural increase of 26,900 and net migration gain of 900.
Auckland and Carterron areas had strongest growth, with smaller increases for Wellington, Hamilton and Palmerston North. Of the 43 North Island territorial authority areas, about half recorded a population decrease.
The largest rates of population decrease were in Opotiki (down 2.6%) and Wairoa districts (down 2.5%).