The New Zealand population is expected to get a whole lot older in the next few decades, according to the latest Statistics New Zealand report.
The number of people aged 85 years and older will more than triple, from about 83,000 in 2016 to between 270,000 and 320,000 in the next 30 years, the report says.
It also predicts the population of over-65s will roughly double - from around 700,000 now to between 1.3 and 1.5 million in 2046.
As the population ages and the gap between births and deaths narrows, overall population growth is expected to slow to less than 1 percent in the 2030s.
New Zealand's population is likely to hit five million around 2020, but could reach the milestone even sooner, the report says.
In the year ended June 2016 the population grew at its fastest rate since the early 1960s, jumping 2.1 percent, or 97,000 people.
"Our population was estimated to be 4.69 million at 30 June 2016, with net migration being 69,100 over the June year," Stats NZ senior demographer Kim Dunstan said.
The latest forecasts show a high chance of the population rising to between 4.9 and 5.1 million by 2020, and reaching between 5.3 and 7.9 million by 2068.
The figures show New Zealand's median age has risen from 25.6 years in 1970 to 37.1 years old in 2016.
By 2068, Stats NZ predicts half the population could be older than 46 years old.
The rise in median age is heightened by the large number of people born between 1950 and the early 1970s moving into the older ages, but the report says baby boomers are not to blame.
It's caused by society's change towards lower birth rates and lower death rates.
The projections indicate that once baby boomers have passed on, the New Zealand population won't revert to a younger age structure unless there's a major rise in fertility rates.