Fog restrictions were put in place at the airport about 6.30am on Wednesday.
Eleven regional flights from Auckland were cancelled and 19 were delayed.
Five flights to and from Christchurch and one to Queenstown were also facing delays.
No international flights have been affected so far.
Travellers were advised to check with their airline for the latest updates on their flight.
MetService meteorologist Oscar Shiviti said the fog should clear by noon and fine conditions were expected for the rest of the day.