About 12 domestic flights to the regions have been cancelled and a further 17 delayed due to the fog around Auckland Airport.
Arrivals and departures from the Bay of Islands, Gisborne, Great Barrier Island and Kaitaia were among the flights delayed.
Flights from Palmerston North, Tauranga, Napier and Nelson, and flights to Wellington, Taupō Napier and Great Barrier Island were among the cancellations.
An Auckland Airport spokesperson said international flights hadn't been affected.
Domestic flights to Christchurch, Dunedin, and Queenstown were also going ahead as planned.
The fog also cancelled some Auckland ferry services, including between the city, Devonport, Bayswater and Half Moon Bay.
It's the third morning in a row that Aucklanders had woken to fog, forecaster MetService said.
"Latest satellite imagery shows fog from Auckland to Central Plateau, and should clear later this morning. Fog is unlikely to redevelop tonight in Auckland."