The net population gain from migration last year was a record 50,900.
"It is too early to tell if migration inflows have peaked," ASB economist Chris Tennent-Brown said.
Departures appeared to have stabilised over the past six months at about 4,700 a month but December was the first month to record a significant dip in arrivals in well over a year, he said.
Arrivals in December were 8,830, a 9.9 per cent drop from the November figure. The decline is almost entirely explained by a drop in the number of people arriving on student visas.
Westpac economist Felix Delbruck said: "At this stage we are inclined to take the December drop with a grain of salt. Seasonal factors can make the underlying trend hard to gauge around this time of year. December is typically a slow month for student arrivals, before their numbers surge in January-February."
Last year's net gain of 50,900 was up from 22,500 in 2013 and net losses in the two years before that.
The net loss of 3,800 people to Australia last year was down from 19,600 in 2013 and less than a tenth of the recent peak of 38,800 in 2012.
It mainly reflected fewer New Zealanders leaving for Australia but also an increase in the number returning.
"The attractiveness of the New Zealand labour market relative to Australia's and the rest of the world's has been, and will continue to be, a key influence," Tennent-Brown said.
The number of immigrants - defined as those intending to stay for at least a year - who entered on student visas jumped 49 per cent to 22,900 last year.
That included an increase from 4,400 to 8,500 in Indian students.
Of the annual net gain of 50,900 migrants last year, nearly half (23,000) occurred in Auckland.
