The 2017 Asia-Pacific Economic Cooperation meetings are scheduled to be held in Vietnam on November 11 and 12.
Asked if the way to ban buyers was via a tax, she said the only tax option was stamp duty, "and have been told that won't work".
When asked if the Government backed a sugar tax, Ardern said "we have always backed reducing sugar in our foods".
She said she thought people would be surprised at the amount of sugar in food, "across number of food items, not just drinks".
She said the Government would work with industry to "bring that rate down" but said it was leaving all options on the table.
When Hosking asked how a new tax could be implemented given the promise not to introduce any new taxes before 2020, Ardern said: "We will make use of all existing options".
Hosking also quizzed the Prime Minister about plans to introduce a petrol tax to help pay for Auckland infrastructure, asking if it was a mechanism other councils could also use to raise funds.
"Auckland is our focus. That is where the need is," Ardern said.
She said there was a need to do "quite a bit of investment" in the city and there was "a gap in the funding plan".
When pushed about whether other councils could ask for a similar levy, she said the government "haven't thought about it" but "I guess the issue" is that if you approve such a mechanism for one council, you may have to for others.
She reaffirmed the government would move to ensure the current levy was restricted to Auckland.
When asked about so-called work-for-the-dole schemes, Ardern said Labour's plan had always been called "ready to work" and involved work experience for long-term unemployed people.
She said it was different to work-for-the-dole but would have a similar impact.
She said fair pay agreements were "not in our 100-day plan" and so were "not first cab off the rank".
Ardern confirmed the Government does want to "sit with employers and unions" to discuss wages which "will take some time".
