Thick fog at Auckland Airport continued to cause problems for air travellers this morning with domestic flights delayed.

It was expected to clear soon after sunrise but airport authorities said although the fog lifted briefly, it returned and by shortly after 9am 30 domestic flights had been affected some delayed and others cancelled,

Passengers on all cancelled flights were expected to be re-booked on later flights.

International flights were briefly delayed but were back on schedule by 9am, said an airport spokeswoman.