Flights are cancelled at Wellington Airport and most international arrivals diverted until 6am, with heavy rain affecting poor-visibility landing systems.
Some domestic flights had been diverted or delayed, and others had been cancelled.
The airport said all international arrivals into Wellington would be diverted and all flights had been cancelled until at least 6am tomorrow.
Airways spokesperson Emma Lee said the instruments that were affected helped pilots land when visibility was poor, something that was crucial in heavy rain.
She said it could be up to two hours before the systems would be running again, and international flights arriving at midnight could be diverted.
One Qantas flight from Sydney landed at 12.44am.
The instruments stopped working about 8pm.
The airport said passengers would be looked after, but some might have to stay overnight at the terminal. No further updates would be available until 6am.
Flight information would be available at the airport website.