A 20 per cent tax on junk food to fund free dental care for low-income families is being proposed by one of New Zealand's minor parties.

The Opportunities Party (TOP) says the tax would bring in about $1 billion a year which would also be used to cap the cost of doctors' visits to less than $10 and ensure nationwide access to cheap fruit and vegetable boxes.

The 20 per cent tax hike would see the cost of a Big Mac jump by $1.64 to $9.84, a 1.5L bottle of Coke increase by 75c to $4.64 and a slab of Whittaker's chocolate increase by 93c to $5.62.

The party launched its health policy this afternoon outside the Coca-Cola factory in Auckland.

TOP said the 20 per cent tax on junk food and sugary drinks would raise an estimated $1 billion.

That would fund their public health measures to keep the cost of GP appointments to $10 or under, provide free dental visits to adults on the lowest incomes affecting about one in five people and offer cheap fruit and vegetable box schemes.

They would also ban marketing junk food to children.

TOP board member Jono Hoogerbrug, who's also a South Auckland GP, said unhealthy food was a major public health issue and encouraging people to eat healthier would have "major long-term benefits".

He pointed to last year's Unicef report which ranked New Zealand second-worst in the OECD for child obesity with 39 per cent of Kiwi kids classified as being overweight or obese.

"Even our most vulnerable children are asking the Government to take a stand on unhealthy food to help support them and their families.

"As a doctor in Papatoetoe, I see first-hand the consequences of Auckland being saturated in junk food outlets."

Hoogerbrug said TOP would use the existing healthy star labelling system to decide which foods should be taxed and would include lollies, biscuits, potato crisps and sugary drinks.

He said sugar taxes in some form have been implemented in more than 40 countries and were backed by the World Health Organisation and a number of New Zealand health organisations.

In turn, the 20 per cent hike in tax on unhealthy foods would fund cheap doctors' visits which would improve access to preventative care for at-risk populations, said Hoogerbrug.

TOP deputy leader Shai Navot said their plan for affordable dental care for low-income earners would also improve long-term health outcomes and called setting up fruit and veggie box schemes around the country a "no-brainer".

"These schemes are relatively easy to set up and run, and they make it easier for everyone to have access to healthy food choices."