The trans-Tasman bubble will open at 11.59pm on April 18, NZ Prime Minister Jacinda Ardern has announced.

Ms Ardern said any state lockdowns would result in suspended flights and travellers should be aware travel plans could be disrupted at the emergence of cases.

NZ will implement a traffic light system based on specific Australian states rather than a nationwide approach.

New Zealanders have been able to travel to Australia without going into quarantine since October.

More to come.