Director General of Health Ashley Bloomfield said the cost of New Zealand's largest-ever vaccination program kept expanding and would top $NZ1 billion ($A926 million) and perhaps reach double that.

"I think everyone would agree that it's a good investment," he said.

"The initial envelope that was set aside for the vaccine advance purchases was up to a billion dollars. Not all of that is being used.

"The cost of all the rollout right across the country will be probably be half that again.

"That's hundreds of millions of dollars. So probably somewhere between one and two billion, I would have thought that's the total cost."

Jacinda Ardern's government made Pfizer their primary vaccine provider in early March, steering clear of the troubled AstraZenica vaccine.

It has not revealed how much the vaccine costs, citing the need to retain commercial confidentiality.

Vaccines will be voluntary and free to every New Zealander who wants to receive it.

The vaccine program is one of two tenets to New Zealand's defence against COVID-19; the other is its border regime, known locally as Managed Isolation and Quarantine (MIQ).

The government has budgeted $NZ1.73 billion ($A1.6 billion) on MIQ in the two years to June 2022.

Dr Bloomfield revealed new details around New Zealand's rollout at the Ministry of Health on Thursday.

MIQ workers, their families, and front-facing health workers are being prioritised in the rollout and are able to be vaccinated now.

As eligibility widens, authorities will focus on remote and rural communities, leaving larger urban centres until capacity grows.

New Zealand is currently administering around 7000 doses a day, which will ramp up to be around double that by June.

Its stated goal is to have delivered 1.16 million doses by the end of June

From there, when the program expands to the general population and more vaccine arrives, Dr Bloomfield said it would hit "50 to 60 thousand a day".

Unlike the Australian government, which has abandoned its vaccination goals, Dr Bloomfield remains "really confident" that every Kiwi will be vaccinated by year's end, if they want to be.

"That is absolutely the plan," he said.

Health officials will encourage volunteers to help with the effort, running massive walk-up clinics.

Dr Bloomfield said GPs would also be key vaccinators and would be encouraged to offer the vaccine "opportunistically" to Kiwis when they go to see their doctor for unrelated health issues.

The government's research indicates around 9.4 per cent of the population "definitely" won't take the vaccine.

Australian Associated Press