Almost 50 flights have been cancelled from Auckland Airport because of fog, and others are delayed.
Fog sets over Auckland CBD. Photo: RNZ / Kymberlee Fernandes
Restrictions implemented at 4am are still in place.
Those cancelled include flights to and from Tauranga, Rotorua, Napier, and Whangārei.
On main trunk routes only two flights each from Wellington and Christchurch have been delayed, and international flights are operating as normal.
Travellers are asked to check the Auckland Airport website for up-to-date details.
Air New Zealand said the fog and the weather around the rest of the country was disrupting services, and that was expected to continue around until lunchtime.
Flights from Kerikeri to Auckland, through the central North Island and to parts of the South Island are affected, with flow-on effects elsewhere.
Air New Zealand said jet planes were running almost as normal.
It said travellers were being offered road transport options where possible.
The fog was also making driving hazardous, with the Transport Agency asking motorists to allow more time and drive with extra care.
Flights on smaller planes to and from regional airports are more likely to be affected than larger domestic flights, such as Wellington and Christchurch.
Yesterday, the fog caused 21 domestic flights to be cancelled, and 20 more delayed, and restrictions lasted until 10.40am.