Migration added a net 3100 people to the population last month, the highest monthly gain since May 2003.

For the 12 months ended January the net gain was 25,700, the highest since the April 2004 year and up from just 12 people the year before when departures almost matched arrivals.

In the latest year 15,900 fewer people left for Australia, while 5000 more returned. The net loss was still 17,100 but that was down from 37,900 the previous year.

"We expect transtasman departures will remain cyclically low through this year while Australian labour market prospects remain weak and New Zealand's continue to improve," said Westpac economist Felix Delbruck.


"While the drop in departures to Australia has been the biggest driver of the stronger net immigration trend, there has also been a noticeable lift in the number of New Zealanders returning and in overseas migrants. Both are holding steady at above-average levels."

The number of arrivals to Canterbury eased in the last six months or so, while more migrants indicated addresses elsewhere on their arrival cards, notably Auckland, Delbruck said.

ASB economist Christina Leung expects net immigration to peak around 30,000 mid-year. "Strong migration will add a plentiful supply of workers, keeping labour market strains low. However, migrant inflows will put further pressure on the housing market, particularly in Auckland."