Net immigration has hit a 10-year high, as far fewer New Zealanders leave for Australia than in recent years.

At the same time, more migrants are arriving from China, with the net gains from that country now topping British migrants for the first time in a decade.

In the year to February, there was a net gain of 29,000 migrants to New Zealand, according to Statistics NZ figures.

The latest net gain was the highest since the 30,100 annual gain seen in the year to February 2004.

The highest ever net migration gain was more than 42,000 in the year to May 2003.

The boom in immigration seen in the early 2000s was a factor in rapidly rising house prices during the period. For the month of February this year alone there were 3500 more migrant arrivals than departures, again the best in a decade.

As fewer New Zealanders leave for Australia and more foreigners arrive here, the trend in migration has been rising since late 2012.

Westpac Bank economists said that at the present monthly rate, it would only take a few more months for annual net immigration to exceed its forecast peak of 33,000.

"So that forecast, which some would have regarded as optimistic a year or two back, is now looking conservative," Westpac said.

A drop in departures to Australia was the main factor behind the current upsurge in net immigration.

"Given the current unusual divergence between Australia's and New Zealand job markets, trans-Tasman departures are likely to remain low for now, though there are early signs that Australian job growth may be picking up again," Westpac said.

The Reserve Bank has forecast a net gain of 35,000 this year.

Strong net migration is seen as a boost for the housing market, but on the other hand, quickly rising interest rates this year and next are expected to take some heat out of the market.

In the February 2014 year, migrant arrivals numbered 96,900, and migrant departures numbered 67,800, resulting in a net gain of 29,000 migrants.

That was much higher than the net gain of 1200 in the February 2013 year.

In the latest year, New Zealand had a net loss of 15,000 migrants to Australia, well down from 36,700 a year earlier, as job prospects worsened in Australia and improved in New Zealand.

Most migrants going across the Tasman, both ways, are New Zealanders.

There was a big rise in New Zealanders leaving for Australia in the wake of the big Christchurch earthquake three years.

Net gains were recorded from most other countries, led by China (6,100), India, and the United Kingdom (each 5,800).

It was the first time for a decade than net migration gains from China have beaten Britain. But there was also a big influx of Chinese migrants between 1996 and 2004, when many of them were students.

Now the mix is different with a smaller proportion of migrants under 24 years and more people who are 50 and older.