Migration to New Zealand remains high, but is down more than two percent from the peak reached earlier this year.
For the year ended October there was a net migration gain 70,700, the lowest annual tally in 10 months. The number of permanent migrants peaked at 72,400 in July.
However, the fall was mostly due to the record 27,400 non-citizens who left New Zealand in the year ending in October.
"Given that the surge in foreign arrivals began in 2013, we have been expecting to see a corresponding surge in departures," Westpac senior economist Satish Ranchhod said.
"This trend looks likely to continue for some time yet, and will drive a substantial downturn in total net migration over the coming year."
Mr Ranchhod said changes to policy by the incoming government would add to the natural slowdown.
Westpac has forecast immigration gains to fall to about 10,000 by 2021, which would reduce population growth and economic activity.
Statistics New Zealand said the high net migration was still being driven by the arrival of non-citizen immigrants.
It said a seasonally adjusted 5580 people settled here in the month of October, the first rise in three months.
Prime Minister Jacinda Ardern said the government's changes to immigration would not be part of its 'First 100 Days' plan, but work was under way.
"Focus for us of course was on the settings, so a lot of a discussion around the numbers, [but] for us it was about making sure that those who choose to call New Zealand home are getting the best opportunity possible," she said.
"That means making sure the work - that they've had an undertaking is available - is available, and that our students in particular aren't being exploited."
Visitor numbers to New Zealand were also breaking records, rising eight percent last month compared from the year earlier.
Arrivals from Australia over the past year rose five percent, with visitors from the United States also up strongly over the year before.