New Zealand's estimated population will hit the symmetrical figure of 4,444,444 some time on Thursday, Statistics New Zealand says.

"While the new resident could be a New Zealander flying home after living overseas, or a new migrant, they're most likely to be a new baby, as that's where most of our population growth is coming from," population statistics manager Andrea Blackburn said.

"It will also pass quite quickly. The population is currently growing by roughly 100 people every day, so it will only be at 4,444,444 for about quarter of an hour."

Such landmarks were quite rare, she said.

New Zealand's population hit 3,333,333 in the mid-1980s and probably won't get to 5,555,555 for another 30 years.