New Zealand Prime Minister Jacinda Ardern says a ban on foreigners buying existing homes will begin in early 2018, but won't apply to Australians seeking to buy homes across the ditch.

It comes after the NZ Labour leader, who formed a coalition government earlier this month, announced her first trip as PM will be a trip to meet Malcolm Turnbull.

Ardern will meet the Australian PM on Sunday in Sydney before returning to Wellington later in the day.

The pair are expected to discuss trade and defence ties ahead of the upcoming APEC and East Asia Summits.

Ardern told reporters the housing legislation will be introduced by December 25.

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