Airlines are working to clear a backlog of flights as fog lifts from Auckland Airport. 

Spokesman Richard Lewellyn says all flights in and out of the airport have now resumed. 

However, there are still some delays for flights to some regional destinations.

Earlier, 21 flights were cancelled and 13 were delayed or rescheduled due to heavy fog.

Mainly regional flights are affected but international and domestic services using jet aircraft can operate in fog.