New Zealand is threatening to undershoot the number of migrants it needs to keep the economy healthy, say immigration consultants.

Immigration New Zealand has returned its lowest number of "expressions of interest", after a period of six months where selections have been around 30 per cent lower than previous years.

If the trend continues, less than 13,500 applications will be selected this year.

The numbers of skilled and business migrants finally approved could fall far short of the 27,000 to 30,000 people the New Zealand Residence Programme targets, an immigration commentator has said.

Mike Bell, who runs the online move2nz site, says this is the lowest selection since the present rules were introduced in 2005.

"At this rate, it suggests that an additional 5500 people would be required to meet the minimum numbers under the quota," said Mr Bell.

The direct financial impact on New Zealand of fewer skilled migrants coming could be a loss of more than $1 billion, because an average migrant family spends about $200,000 in New Zealand to start their new lives.

But other immigration observers say the impact could be greater, as it would leave New Zealand short of skills in vital industries and stall economic growth.

"This is worrying. There may be concerns for jobless New Zealanders but slashing skilled migration numbers is not the solution," said Dr Henry Chung, senior marketing researcher at Massey University.

Immigration expert Paul Spoonley says the global economic crisis has also resulted in a reduced number considering migration, and this could impact on migration numbers to New Zealand this year.

But head of Immigration Nigel Bickle says it is on track to meet immigration targets, despite the low selection on July 14.