Communications manager Melanie Nunn says it's only impacting the smaller turboprop planes.
She says one flight to Dunedin and one to Christchurch have been delayed so far this morning.
Nunn says people should check flight information on the airport's website and keep in touch with their airline.
She says it's not clear how many other flights will be delayed because it depends on when the fog lifts.
Nunn says visibility is meant to improve at 10am.