New Zealand tax residents pay New Zealand tax on their worldwide income.
This means New Zealand’s tax rules apply to any residential property New Zealand tax residents buy or sell in other countries. They will also include the overseas income in their New Zealand income tax return and pay any tax if that property sale would be taxable in New Zealand.
If they're a New Zealand tax resident who earned income selling a property in another country, they may need to pay tax there under that country's tax rules.
It is possible to get credit for taxes paid overseas on the same property if a double tax agreement (DTA) is in place with that country.
Overseas property sales also come under the bright-line property rule.
If this situation applies to you and you need advice, contact your tax advisor.