Frustrated passengers have done an entire round-trip from Wellington to Dunedin and back again tonight without ever touching down.

Fog at Dunedin Airport appears to have forced Air New Zealand flight 691 to turn back just minutes from landing.

Flight radar shows the plane flew some 1300km and spent 2hrs and 16 minutes in the air for what should have been a 55 minute trip.

It had already left Wellington Airport two hours late due to the backlog of flights caused by the grim weather in the capital today.

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MetService meteorologist Hannah Moes said weather conditions at Dunedin Airport had been fluctuating throughout the evening, and visibility had steadily fallen as fog descended from about 10pm.

Showers and cloud were passing through and could lift visibility "a little", Moes said.

"We expect conditions to continue fluctuating throughout the night in and out of fog. At this stage we don't know when it might lift."