The government is being accused of being beholden to the junk food industry and the opposition says the country's poorest children are paying the cost.
An annual snapshot of the nation's health shows 31 percent of adults are now obese and problem drinking is increasing.
The Health Ministry's Health Survey has found one in nine children aged two to 14 are obese.
Children living in the poorest neighbourhoods are five times more likely to be obese than those living in the most affluent.
More than five percent of the adult population is now morbidly obese, up from 3.4 percent five years ago.
Green Party co-leader Metiria Turei said the statistics revealed how deep into the pockets of the junk food industry the government was.
"They have dismantled so much of the good work that was done by the previous government in trying to improve children's' health. This National government will not regulate for children's' health and as a result we're seeing these terrible statistics of increasing obesity for the very poorest."
She said the refusal to deal with the causes of obesity meant the health system would have to pay a lot more in dealing with the effects.
"We all know that, that's why you have preventative measures in place, but this government refuses to deal with the concept of a soft drink tax for example, it dismantled the healthy food in schools programme, it won't deal with advertising of junk food to children on television and just very recently New Zealand's leading expert on fighting obesity quit in disgust because she can't get any decent policy out of this government."
Mrs Turei said the end result was really unhealthy kids and a long-term cost to the health budget, she said children's health, particularly in poorer areas, was worsening under National.
She said the Green Party had long advocated for the removal of advertising of junk food during children's programmes, and that there needed to be a conversation about a tax on soft drinks.
In 2009 the Government scrapped a rule which stated schools which sold food and drinks could only make healthy options available, saying schools were no longer required to be food police.
The same year the government stopped funding the Obesity Action Coalition and the organisation ceased to exist in 2010.
And the Healthy Eating Healthy Action programme introduced by the former Labour Government in partnership with the Green Party was also wound down.
Labour Party health spokesperson Annette King said the statistics were the warning that the country had been having for the last decade that something must be done about the obesity problem.
"I'm really concerned that we've wasted eight years in terms of doing anything about obesity since the government's been in after they cancelled all programmes, and what they have put in place is timid. They are not treating obesity with the seriousness that they ought to."
Ms King said the Government had backed itself into a corner when it scrapped much of what had been put in place by the previous Labour Government, labelling it nanny-state.
"They've got to a bind now it's hard to get out of without looking like nanny-state. They've got to get over themselves and think about the health of New Zealanders rather than their own political backsides."
Minister of Health Jonathan Coleman was unavailable for comment.
However, the government did recently [http://www.radionz.co.nz/news/political/287423/government-tackles-childhood-obesity
introduce a new plan aimed at tackling childhood obesity], which included intervention for children as young as four.
Under the plan, 95 percent of children identified as obese would be referred to a health professional for clinical assessment and family based nutrition, activity and lifestyle interventions.
Dr Coleman said at the time of the launch the government was working with the food industry on the role it could play, including appropriate marketing and advertising to children and food labelling.