"This will apply to people enrolled in both Very Low Cost Access practices and other practices."
Labour said Kiwis who are on the Very Low Cost Access scheme or are Community Service Card holders will have their maximum fee cut from $18 to $8, and costs for teenagers will drop from $12 to $2.
Under-13s will remain free.
As part of the policy the Community Services Card will be extended to another 350,000 New Zealanders.
Adults and teenagers who are not on the low-cost scheme will get a $10 reduction in their fee if their GP practice chooses to take up the extra funding offer. Labour said this would reduce the average fee from $42 to $32.
Ardern said funding for the policy would come from the $8 billion of increased health funding pledged by Labour over the next four years.
"GP practices will also get a further $46m over and above the funding to reduce fees, a 5 per cent increase on current funding... Labour will also invest $30m over three years to boost the number of GP training places to 300 a year.
"This initiative will cut fees for New Zealanders while we undertake a full review of the primary care system aimed at better targeting subsidies, ensuring practices' financial sustainability, and reducing other barriers to access. This review will keep zero fees for under-13s and look to further lower fees for others," Ardern said.
Labour said its GP policy would cost $259m per year.
The announcement was met with cheers by crowds of hundreds at the Mangere town centre. Pacifica children were more likely to develop rheumatic fever, which Ardern described as a national shame.
"We know that will make a huge, huge difference," Ardern told crowds.
National Party campaign chair Steven Joyce said Labour's policy was a copy of National's announcement earlier this week, with a $10 universal subsidy tacked on.
"That's the level of thought they have put into it. Targeting low-income New Zealanders is a good idea, which is why we announced it. But for every other New Zealander it's a poor exchange.
"If Labour commited to National's Family Incomes Package families would put some of the money towards a doctor's visit one week, and something else they need the next week. Why can't they trust people to make more of their own decisions."
GP fees - how Labour says they will change under its policy
Very Low Cost Access practices:
• 13-17-year-olds: From $12 to $2
• Adults: From $18 to $8
Other practices that sign up to the extra funding:
• 13-17-year-olds: From $30 to $20
• Adult: From $42 to $32
