WELLINGTON, Feb. 15 (Xinhua) -- The provisional estimate of annual net migration in the year ended December 2018 was 48,300, which is estimated to be lower than a year earlier when it was 52,700, New Zealand's statistics department Stats NZ said on Friday.

Migrant arrivals were provisionally estimated at 145,800 and migrant departures at 97,500, Stats NZ said.

The last five years, 2014-2018, had the largest net migration gains ever in New Zealand's history with an estimated 270,000 more migrant arrivals than migrant departures. An estimated 700,000 migrants arrived and 430,000 migrants departed over this period, it said.

Over the five years, most migrants arrived on work, visitor, or student visas. However, by definition, they stayed for at least 12 months after extending their visa or transitioning to other visa types, including residence visas, population insights senior manager Brooke Theyers said in a statement.

"Even though many migrants arriving only stay for a year or two, it's important to count them as migrants and not short-term visitors. They are part of our resident population, which has implications for infrastructure and service provision," Theyers said.

Annual net migration has gradually fallen from the record peak of 63,900 in the year ended July 2016. This reflects an increase in migrants leaving New Zealand over this period, in particular, non-New Zealand citizen departures, she said.