More than 40 flights into and out of Wellington Airport are tonight affected by fog.

All airlines are affected - even some international flights are involved.

Air New Zealand is asking travellers to check its website for details of disruptions.

Meanwhile, Jetstar said one of their flights from Melbourne was diverted to Auckland.

The disruptions also mean travelers aiming to fly to Wellington from airports around New Zealand are also grounded.

Witnesses have reported particularly large crowds of capital-bound travellers stranded in Auckland.

MetService said Wellington's fog around the south coast will spread this evening, and more is forecast for tomorrow.