The Green Party's promise of free healthcare for everyone up to the age of 18 is unaffordable and fiscally irresponsible, the Government says.
Greens co-leader Metiria Turei made the policy pledge to about 200 members at their annual conference in Upper Hutt on Saturday morning, saying it would cost about $29 million a year.
The party was confident the pledge was affordable, if it formed part of the Government after September's election.
The Government promised in its 2014 Budget to extend free GP visits to children up to the age of 13 from July 2015.
Ms Turei said the Greens would extend that to the age of 18, and wipe all prescription charges, as cost should not be a barrier to young people getting the healthcare they needed.
The Green plan would reduce hospital admissions, help prevent unwanted pregnancies, and support young people through a complicated time of their lives, she said.
The party would roll out its extension from July 2015 so it dovetailed with the planned extension to 13.
But Health Minister Tony Ryall said the party needed to front up with some details on how that would be achieved.
"What taxpayers are seeing is a bidding war on the left, as they try outdo each other in the promises that they're wanting to make.
"But in the end, they're not telling New Zealanders how they're going to pay for them."
The Greens had already promised $250 million a year extra for health, Mr Ryall said.
Greens co-leader Russel Norman told the Sunday programme the money would come from cuts in other areas and some new revenue.
"It's a combination of cuts in some areas, so for example we would re-prioritise money away from the Roads of National Significance - there's opportunity for cost savings there, Dr Norman said.
"We support, and have long supported, a capital gains tax, so that's a source of revenue for the Crown."
Medical Association General Practitioner Council chair Kate Baddock said free health incentives should be for those who really need it, such as the elderly and others with high needs.
"We're talking about those who live below the poverty line, we're talking about those who have significant need and can't access the healthcare that they require.
"We are talking about the vulnerable but the vulnerable of all ages."
Dr Baddock said the Green Party's policy appeared to be a good idea but she questioned about its financial viability.
Meanwhile, the party will announce a major environmental policy on Sunday afternoon which it will campaign on heading into the election.