Aging baby boomers are pushing numbers of those aged 65 and over to unprecedented levels, adding to the financial pressure on the rest of the population.
The age group makes up 14 per cent of the population and continues to rise - outgrowing all other age groups, according to Statistics New Zealand (SNZ) figures.
In the last decade the age group has steadily increased from about 12 per cent to the existing rate.
While the number of those aged 65 and over has increased by 43,100 in the last two years, fertility and mortality rates have dropped.
The result is an increasingly aging population, which has wide-reaching implications, said SNZ project manager population statistics Jo-Anne Skinner.
"You've got the situation with superannuation, and people then moving into an area where they're not actively generating income for themselves.
"The rest of the population has to effectively support that group through taxes and the like," she said.
As the population ages, the health sector will also be affected, creating the need for a changed focus on services including residential care, said Ms Skinner.
Baby boomers are those born during the post-World War II baby boom between 1946 and 1964.
As they reached retirement, the effects of an increasingly aging population were "starting to hit home now," she said.
Numbers of those aged 0-14 have dropped by 3400 in the last two years, and the 15-39 group had dropped by 1500.
By 2036 the country's population is expected to reach 5.4 million, according to SNZ projections.
Twenty-five years after that the median age of Kiwis could exceed 44 years. The existing median age is 38.2 years for females and 35.7 years for males.