Speaking on Newstalk ZB this morning, the Prime Minister reiterated his opposition to a foreign buyers register, but said a stamp duty or land tax on non-resident buyers was a possibility.
He said prices were "definitely going up more rapidly than Government would want".
This trend was not unique to Auckland, and was also occurring in other large cities including Sydney, Melbourne, Dubai, London and New York.
"Why? Because it's attractive," Mr Key said. "So it's like a lot of things in life. Be careful what you wish for, because if house prices start falling in Auckland it may be a reflection that it's a less attractive place to be."
He went on to say that many Aucklanders already owned homes and wanted prices to rise.
"Aucklanders are getting wealthier. I tell you why they're on the front page of the newspaper every day. I don't want to be unkind to news outlets that run these stories, but the truth is, people are interested.
"They either own a home, want to buy a home, or have sold a home. It generates interest in their magazines and their newspapers.
"The point is there is over 500,000 Aucklanders that own a home. They are significantly wealthier.
"I go around the rest of the country and people say to me 'Can we have a few of those Chinese buyers in Wellington and other parts of New Zealand because actually we want our house prices to go up'."
The Government's primary focus was on increasing supply, and since the building boom in Christchurch house price inflation had begun to fall.
Mr Key said Aucklanders might not welcome a similar trend.
"Let's just take the counter-factual for a moment. Would you want your house price going down?
"And what most Aucklanders say to me is 'I'd rather my house price went up, but I'd rather it went up a little more slowly than this'."
He conceded that rising house prices were contributing to increases in the costs of other goods.
"There's no question when you get house price inflation then it feeds into the Consumer Price Index and therefore inflation stays a bit higher."
But he said that inflation levels were relatively low - about 0.2 per cent at present.
Labour's housing spokesman Phil Twyford said the Prime Minister's comments showed how out of touch he was.
"John Key claims Aucklanders want the value of their homes to keep rising. But for most, that paper wealth won't be realised unless they sell up and move cities."
Mr Twyford said even people who owned houses were concerned that their children and grandchildren would never be able to own a home in Auckland.
He said the Prime Minister was speaking on behalf of those who owned property, but the majority of Aucklanders were renting.
The Labour MP said no one wanted to see Auckland house prices collapse, but the Prime Minister had a duty to also represent young New Zealanders who were unable to get onto the housing ladder.
