A Jetstar flight bound for Nelson circled the airport numerous times with "pea soup" fog preventing it from landing.
The Flightrader24 site shows JQ394 left Wellington at 3.35pm on Monday.
The flight to Nelson usually takes 26 minutes, but the plane was in the air for hours, spending much of the time circling Nelson airport waiting for fog to clear.
The plane, a Bombardier Dash 8, was due to land in Nelson at 8pm, according to the airport's website.
The Wellington, Auckland and Nelson Airport websites show a handful of other flights to and from Nelson have been cancelled.
Nelson Airport terminal supervisor Simon Trillo told the Nelson Mail that at 5.30pm the plane was still circling.
"They can't get in, the fog is a bit too low.
"We're open, but it's up to the pilots. It is what it is, it's unfortunate, but it happens at this time of year."
The fog at Nelson Airport is like "pea soup" right now with very low visibility, MetService meteorologist Sarah Sparks said. The fog rolled in around 6pm after a spell of low cloud.
She said it was very unusual for Nelson Airport to have fog.
"It's forecast to clear later tonight but it's pretty hard to give an exact time," Sparks said.
"[The wind] has turned southwesterly there, so we're hoping that will dry it out and clear the fog."
Fog could also descend on Dunedin and Invercargill later tonight but Christchurch was likely in the clear due to showery rainfall.