WELLINGTON (Reuters) - New Zealand Prime Minister Jacinda Ardern said on Tuesday a ban on foreigners buying existing homes would begin in early 2018, but the restrictions would not apply to Australians.

New Zealand's Prime Minister-designate Jacinda Ardern speaks as she stands next to New Zealand Green Party leader James Shaw in Wellington, New Zealand, October 24, 2017. REUTERS/Nicolaci da Costa

Ardern campaigned in the recent New Zealand election to restrict foreign buyers to reduce demand, while the country tackles what her Labour party says is a housing crisis left unresolved by the previous National administration.

“We are determined to make it easier for Kiwis to buy their first home so we are stopping foreign speculators buying houses and driving up prices. Kiwis should not be outbid like this,” said Ardern in an emailed statement, using the colloquial term for New Zealanders.

The politically sensitive housing crunch has seen prices rise more than 50 percent nationally in the last decade. In the city of Auckland, prices have almost doubled in that period. The central bank sees fast-rising prices as a major economic risk.

The ban would not apply to Australians, Ardern said, given New Zealanders are exempt from home ownership restrictions in neighboring Australia, where many New Zealanders live.

Ardern told reporters that legislation would be introduced in parliament by Dec. 25.

The restrictions were being fast-tracked so that Labour would not have to renegotiate foreign investment provisions in the Trans Pacific Partnership (TPP) deal, after a long series of talks to revive the agreement since the United States pulled out in January.

The TPP currently requires its 11 member states to give foreign investors equal treatment to locals unless there are specific exemptions.

New Zealand had no such grounds for an outright ban on overseas investment in housing, but its Overseas Investment Act is exempted from the trade deal.

By adding housing to that legislation, Labour will be able to go ahead with the ban without having to request any changes to the TPP when ministers meet on the sidelines of Asia-Pacific Economic Cooperation meeting in Vietnam next week to finalize the agreement.

Ardern said that New Zealand would instead focus on renegotiating rules allowing investors to sue member countries included in the TPP, though she acknowledged it would be difficult to get large changes so late in negotiations.

Some government figures show the number of home sales including foreigners is only around 3 percent, though Labour has criticized that data and says it excludes many types of owners, including those who purchase property through trusts.

“It is very important that we preserve these rights for New Zealand,” Trade Minister David Parker told reporters.