A demographer says the continual setting of records on net migration is extraordinary.

New Zealand's annual net gain of migrants has set records for the last 17 months, with an unadjusted figure of nearly 65-thousand in the December 2015 year.

Annual net gains from Australia continued to increase, with 800 migrants, the highest net gain since the October 1991 year.

Demographer Paul Spoonley said it's outstanding it's continued for this long.

"Well I think it's going to continue through the early part of this year, quite what happens later in the year I don't know but this appears to be the new normal."

Mr Spoonley said a lot of migration from Australia is driven by jobs and the fact Australia is not doing so well economically.

The Prime Minister said he believes the fact net migration to New Zealand continues to rise is a positive thing.

John Key said a lot of them are Kiwis coming home and people who are needed in the skills category.

"And on top of that they bring capital and ideas and all of that sort of stuff. So countries that are doing well attract people."