Heavy fog grounds flights in Brisbane

A blanket of fog that descended over Brisbane overnight has grounded dozens of flights and forced many others to be diverted.

Flyers were left stranded and in disarray after a total of 80 flights were cancelled and another 30 were diverted because of the fog.

"It's very unusual to see fog that early in the evening. Just that moisture building up through the day meant that the atmosphere was very saturated and primed for that fog to develop," Rick Threlfall from the Bureau of Meteorology told 9NEWS.

Brisbane Airport Corporation said it was the most significant fog event they have ever had to deal with. 

The end of the school holidays puts extra pressure on airlines, with many more passengers than usual needing flights to get home.

The fog was readily apparent for rugby fans at Suncorp Stadium, who struggled for a clear view of the Reds v Brumbies game last night.

Conditions in Brisbane cleared by sunrise with the city reaching 22 degrees.