Support for returning the drinking age to 20 is gaining momentum as MPs face calls to address binge drinking.
But politicians courting the youth vote are cautious, and the Green Party has indicated it is unlikely to back a change to move the age from 18 to 20.
MPs are expected to vote on the purchase age provisions of the Alcohol Reform Bill in the next couple of months.
The drinking age was lowered to 18 in a 1999 conscience vote. Health leaders want it restored to 20, saying the evidence points to that as the only option.
National MP Jackie Blue said straw polls had shown "overwhelming" public support for the age to be set at 20.
The Alcohol Reform Bill purchase age provisions would allow 18-year-olds to buy alcohol in licensed premises, but restrict off-licence purchases to those 20 and older.
National MP Tim Macindoe, who wants sales in any venue restricted to 20-year-olds, said support for the move has grown over the past three years.
"In the previous Parliament I would have been struggling for much more than 20% (support from MPs), but at the moment it would be closer to 30. And there will be an opportunity as the pressure comes on over the next couple of weeks to lift that.
"There is support within my own caucus, and there is some support within Labour, as well as [Act's] John Banks, and potentially New Zealand First."
The Maori Party also supports raising the purchase age to 20 for both licensed premises and liquor stores.
National and Labour MPs will be able to cast a conscience vote but the Greens, who have 14 MPs, have yet to decide, although party policy is to oppose raising the age.
Winston Peters said his party had opposed reducing the age to 18 in the first place, and would push for a return to 20.
Meteria Turei said the Greens had a policy of keeping it at 18. "I will be voting, assuming it is a conscience vote, to keep it at 18."
Banks said he had warned of the "stupidity" of lowering the age initially "and now we are reaping what we have sown".
Dunne said he supported 18 with no exceptions. "Lifting the age will prove unworkable, and the split on premises and off-premises idea will be hard to enforce. It's likely to shift business from supermarkets to the licensed trade, with minimal impact on consumption."
Macindoe said he would table his proposed amendments when the bill was brought back in front of the House. At the same time Nikki Kaye will table a paper calling for the age to stay at 18.
"If someone can be elected to Parliament, get married or join the army, then they should be able to buy a bottle of wine," she said.
Macindoe believed the majority would go for the "default option" of the split age.
"It's my hunch that the majority will still go for the split age option. But I'm picking up quite a bit of support for my amendment to go back to 20 across both categories.
"The least favoured option is to keep it at 18, and that is because of the overwhelming public message to make a change."
Alcohol Healthwatch director Rebecca Williams said she "absolutely" supported raising the age, and the evidence supported making it 20 across the board.
"It is not about 18-year-olds, it is about 13-year-olds and making sure they don't begin drinking in their teens."
National Addiction Centre director Doug Sellman said returning the drinking age to 20 was "the only response".