Professor Bedford said natural increase, rather than net migration, still remained the most important factor for population growth.
"Over the whole [Census] period, April 2006 to March 2013, we had a net [migration] gain of just under 51,000, natural increase over that period was substantially greater."
The average number of births is about 60,000 annually while there are about 30,000 deaths.
But "churning" - the process of citizens of other countries replacing New Zealand citizens - meant the migrant workforce was of growing importance to the economy.
"Churn is most significant among the age group most likely to move, 20 to 40 years," Professor Bedford said.
Statistics New Zealand figures also showed that between 2008 and 2012 there was an increase of 81,100 in the workforce who were not New Zealand-born.
Of the 583,300 overseas-born workers, who formed 36 per cent of employees last year, 331,600 were not recent migrants but had lived here for more than 10 years.
Edwina Pio, professor of diversity at AUT University, said she expected the number of minority ethnicities to have increased significantly between the two Censuses.
Demographic changes meant New Zealand employers needed to make drastic changes to the way they viewed employing migrants.
Multicultural development required them to make "seismic shifts in their views towards employing and progressing ethnic minorities in the workplace", said Professor Pio, who is also an associate director of the NZ India Research Institute.
"Employers will need to learn how to manage diversity in the workplace and to see this as a benefit rather than a deficit."
Massey University sociologist and immigration expert Paul Spoonley said the global financial crisis reduced the number of immigrants arriving and contributed to the number of New Zealanders and immigrants leaving, especially to Australia
"In five of those seven years, we had major net losses to Australia ... it looks as though the net loss was about 150,000, so that affects the net gain/loss for New Zealand as a whole," Professor Spoonley said.
It was hard to know if the high number of overseas-born workers showed employers here were now more accepting of migrants.
"Remember that many more of our employers are themselves immigrants who then employ other immigrants," he said.
Statistics did not answer the "real questions" about the nature of this employment, salary levels and if the jobs reflected the qualifications and experience of immigrants.
