New Zealand's population hits 5 million

As the COVID-19 pandemic hit, Prime Minister Jacinda Ardern said we'd take on the challenge as a "team of 5 million" - and new figures showed her timing couldn't have been better.

Statistics NZ on Monday said New Zealand's population passed 5 million in March as the country went into lockdown.

"This is a significant event for New Zealand," said population insights senior manager Brooke Theyers.

"It is also the fastest million in our history, taking 17 years after reaching 4 million in 2003."

At the end of March there were 5,002,100 people living in New Zealand. The exact date we crossed the threshold won't be known until more analysis is done, Statistics NZ said.

The agency had previously predicted we'd reach 5 million sometime in 2020. 

The milestone was reached partly thanks to tens of thousands of Kiwis rushing home before the borders were closed.

"It is most likely the 5 million milestone was reached by a migrant arriving by plane, but could have been reached by a newborn baby," said Theyers.

Since the census in 2013, we've added about half-a-million people - an average increase of 1.8 percent a year, half of it migration and the rest natural increase. 

"The global COVID-19 pandemic has caused unusual international travel and migration patterns in recent months," said Theyers.

"Net migration has been boosted by more New Zealand citizens returning home after living overseas. At the same time, New Zealand citizens may have been unable or reluctant to head offshore."

There's even a chance we could dip back below 5 million "if recent migrant arrivals head back overseas once border restrictions are relaxed and international travel resumes".

More than 1 million people living in New Zealand now were born overseas, and hundreds of thousands of New Zealand-born people live overseas, mostly in Australia.

Statistics NZ says other countries with populations between 5 and 6 million include Costa Rica, Denmark, Finland, Norway, Singapore and the Slovak Republic.

The current best estimate for when we'll reach 6 million is in the 2040s, but that could come sooner or later depending on migration and birth rates. 

"Sustained lower birth rates and an ageing population mean that the population is likely to grow at a slower pace in the future, than it has in recent decades," Statistics NZ said.