Key Points:

Immigrants can be four times more valuable to the New Zealand economy than those born here, an immigration conference in Wellington has been told.

Academics and researchers at the conference, "Pathways, Circuits and Crossroads", said that while immigrants were blamed for many things - from soaring house prices to soaking up social and health benefits - in truth they were vital contributors to economic growth.

Experts warned that New Zealand's economy could be headed for disaster if immigration numbers could not be sustained.

Flashing headlines like "Peters names immigration as key driver of inflation" and "Pacific migrants drain on economy" couldn't be further from the truth, said the Department of Labour's Rob Hodgson.

Speaking on "the economic impact of immigration", he said recent studies had found that overseas-born migrants contributed $8.1 billion to the economy in 2006, while using $4.81 billion in benefits and services. In comparison, New Zealand-born citizens contributed $24.76 billion and used $21.92 billion in benefits and services.

"The net impact for having an immigrant here is $3.29 billion, or $3547 per capita, while the net per capita contribution of a New Zealand-born is just $915," he said.

Recent and established immigrants also paid more income tax than their local counterparts, and migrants generally consumed less in benefits, allowances and health.

Professor Graeme Hugo, from the University of Adelaide, who shared an Australian perspective on coping with demographic change, said it was also wrong to blame migrants for influencing ageing in our societies.

"Immigration policies make migration highly selective by age," he said. "So, the effect migrants have on contributing to an ageing population is, at most, marginal."

Professor Ian Pool, from the Population Studies Centre at the University of Waikato, said it was important for New Zealand to have "sound immigration policies" - not just to attract but to keep migrants here.

Speaking on "Ageing: replacement migration and other demographic responses and policy constraints", Professor Pool said migrants contribute to a country's human capital and policies "must ensure that migration to New Zealand must be continuous and have the characteristics to fill the skills gap we need".

With an increasingly greying population, fertility and births alone could not be depended upon to replace the labour force, he said.

"We need to model our policies to meet two sets of competing demands, that of an ageing population and meeting the needs of the young ready to enter the workforce," said Professor Pool, who told the audience that all his grandchildren had chosen to live outside New Zealand.

Speakers at the conference, organised by the University of Waikato, the Department of Labour and the Office of Ethnic Affairs, include experts from India, Singapore, Australia and the US. Today, the forum takes the theme of family and community in increasingly diverse societies.