The New Zealand population aged 65 and over has doubled since the early 1980s and is likely to double again by 2040, Statistics New Zealand says.
At 635,200, the population aged 65+ now makes up 14 per cent of the population, the National Population Estimate shows.
The population aged 65+ has risen by 48,200 over the last two years as baby boomers - those born from 1946 to 1965 - start to move into the 65+ age group.
"The first of the baby boomers turned 65 in 2011 and we will see this group leading continued growth in our older age groups in the years to come,'' population statistics manager Andrea Blackburn said.
New Zealand's estimated population was 4,470,800 at 30 June 2013. The population grew by 37,700 (0.9 per cent) from the previous year.
Natural increase (births minus deaths) was 29,800, the lowest for a June year since 2005. The low natural increase was mainly due to a lower number of births.
Permanent and long-term net migration for the year was 7,900, which was an increase of 11,100 compared with the previous June year (-3,200).
The increase in net migration was largely due to an eight per cent drop in permanent and long-term departures.