Airlines have cleared a backlog of passengers after fog disrupted flights at Auckland Airport for a second day.

Normal operations resumed at the airport just after 9am on Friday and most of the backlog had been cleared by Friday evening, the spokeswoman said.

However, a few regional flight arrivals were still delayed.

About 40 domestic flights were cancelled or significantly delayed, Radio New Zealand reports.

Two international flights were rescheduled earlier in the day.

The fog also caused problems at Hamilton, Christchurch and Dunedin airports.

Auckland Airport was affected by fog most of Thursday, when normal operations did not resume until about 4.30pm, disrupting the travel plans of hundreds of passengers.