In a strong job market, tourists might get a job in New Zealand and decide to stay, one economist says.

Migration has hit another record but one analyst says we may be underestimating the number of people making New Zealand their home.

Annual net migration reached 72,400 in the July 2017 year, Stats NZ said.

Migrant arrivals numbered 132,100, a new annual record, and migrant departures numbered 59,700 in the year ended July 2017.

SUPPLIED If migration is really running at a rate of 80,000 a year, that might mean more pressure on house prices.

Compared with the year ended July 2016, net migration increased by 3400.

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But Mieke Welvaert, a forecaster at Infometrics, said it was likely that net migration was underestimated by up to 8000 people a year.

"We've analysed a whole bunch of data from Stats NZ that looks at how many people actually do what they say they will do on arrival cards - our current measure of the number of arrivals - and it turns out that when there are lots of employment opportunities, tourists get new visas and effectively become migrants.

"We had this problem back in 2003 when at-the border measures under-measured net migration by 18,000 people."

Infometrics data showed the number of people getting residence visas while they were already in New Zealand had increased 27 per cent since June 2015.

She said that if migrant numbers were higher than the official data showed, that would have implications for infrastructure investment.

Infometrics data showed a lift in migration flows equivalent to 1 per cent of the population could push up average house prices by between 6 per cent and 12 per cent.

Welvaert said Infometrics' research showed an optimal level of migration was about 10,500 to 16,600 people per year.

"That's a far cry from current levels of net migration and not something we think should happen right away, but to lean towards over the next seven to 10 years."

She said a sharp drop in migration could be a problem. Infometrics research suggested that businesses would look to automate their processes as much as they could in that situation.

"We don't think that automation is inherently a bad thing – improving productivity is one way to get more for your money – but we do think that 'turning the tap off' on net migration will impose sharp disruptive change for many parts of the economy.

"As a result, we suggest a more progressive approach to toning down net migration, and to focus migration policy on those that are intending to stay in New Zealand long-term through indirectly or directly obtaining residency."

Stats NZ senior demographer Kim Dunstan said the official statistics were based on people's stated intentions but they usually proved to be a good indicator of long-term movements.

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