While more people continue to move to New Zealand a former Treasury economist says there is no significant economic gain from such high immigration.

Michael Reddell says while it's a sensitive issue now is the time to sensibly discuss our immigration policy without fear of being dismissed as a racist.

In the last year a record 68,000 migrants made New Zealand home and with most settling in Auckland it is changing the way the city looks, sounds and feels.

India leads the migrant numbers with 13,000 over the past year, followed by China, Britain and Australia.

Mr Reddell told Q+A it's not ethnicity but a numbers issue and he would like to see them come down to around 10 to 15,000 skilled migrants - the same per capita level as the US.

"It's very high by international standards. Some of that is the trans-Tasman movement between Australia and here but the core of it - 40,000 - is not and there's no evidence there are any great economic gains from migration," Mr Reddell says.

When New Zealand was opened up to higher levels of immigration 25 years ago, it was promoted in immigration fairs around Asia but now our shop window is the internet and in the last few years four off-shore immigration offices have been closed.

In 2013, the Government tweaked the student visa rules allowing students and their spouses to work and making the transition to residence easier and student numbers have shot up to 27,600.

The unprecedented flow of Kiwis returning home has also driven up the migrant statistics and while Prime Minister John Key says that means we are in good shape, Mr Reddell disagrees.

People from poor countries will always want to come to a richer country. - Economist Michael Reddell

"Frankly I think that's an argument that's got no merit apart from short term politics," says Mr Reddell, adding that while New Zealand is still a relatively wealthy country by the standards of the advanced countries around the world, we're now quite poor.

"They come to us because they can't get in anywhere else. We're richer than the Philippines, China or India so of course many people want to migrate here but if they can get into the United States, Canada, UK or Australia, they'll go there first."

This week Treasury warned that high levels of immigration could push low skilled New Zealanders out of jobs and Mr Reddell argues that we should scrutinise the costs and benefits of immigration.