Immigration appears to be on the rise again - although revisions to the StatsNZ methodology are making it hard for economists to pick a clear trend.

Latest figures, for the year to the end of January, show annual net immigration inflows rose to 58,400 from 56,230 for the year to the end of December.

That was no longer pointing to a plateauing in annual net permanent long term inflows, said ASB economist Mark Smith.

"If correct, this will have widespread market and policy implications," he said.

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The trend in migration has been complicated by a revision to StatsNZ methodology based on new research about how many of our new long-term arrivals actually stay in the country.

The previous data was based on the intended length of stay, as recorded on immigration forms by long-term migrants when they arrived at the border.

While tracking the actual movements of new arrivals is more complex than intentions, Stats NZ now has a system which gives much more accurate data.

The change is related to technology which means we no longer have to fill out the arrival and departure cards when we travel.

That saw the top line immigrant numbers fall sharply.

Net migration, in fact, peaked at 64,000 in mid-2016, not 72,500 in 2017, according to revised figures.

But regardless the past year had seen a slow downward trend.

"Based on today's figures the numbers suggest that net immigration inflows are on a strengthening trajectory, while they had earlier signalled a plateauing in net inflows at historically high levels," Smith said.

January monthly estimates showed a seasonally-adjusted net permanent long-term (PLT) inflow of 6,300 persons, the second highest on record and behind the record December month (revised up to 6,880 persons from 5,070 previously).

Annual net PLT inflows in the 12 months to January rose to 58,381 persons, the highest annual net PLT inflow in 17 months.

Underpinning this were strengthening PLT arrivals, which hit a record 151,619 persons in the January 2019 year.

Migrant departures were estimated at 93,300.

New Zealand citizens were the largest group of migrant arrivals, at 36,400, followed by Chinese with 17,500. Among those departing, 44,100 were New Zealanders, followed by Chinese with 8,500.