The airport says more than 100 flights have been affected by heavy fog in Wellington and at other airports.
People who have been delayed at the airport for an indefinite time have been offered free bottled water.
Travellers who need to stay overnight will be provided with complimentary blankets, water and snacks.
People should check their flight status through their airline or the Wellington Airport website.
Customers currently booked to travel to or from Wellington up until noon tomorrow who do not urgently need to travel automatically have the option to transfer their booking to another date or hold the fare value in credit for up to 12 months toward future travel without the need to advise the contact centre prior to the flights' scheduled departure.
Flights were also cancelled and diverted away from Wellington on Tuesday night due to fog.
Police say the conditions led to a spate of road crashes across the region this morning and caused major traffic delays for commuters.
There were no major injuries but long queues formed on roads after crashes at Pukerua Bay, Johnsonville, and south of the Mungavin ramps.
North Island battered
Drivers caught by rising floodwaters have had to ditch their vehicles after becoming trapped in Auckland as wild weather batters the North Island.
A severe thunderstorm watch had been issued by the MetService for Northland, Auckland, Waikato, Waitomo, Taumarunui, Taupo, Taranaki, Taihape, Wanganui and Manawatu.
The watch would be in place until about 6.30pm, with bands of heavy showers and rain expected over the central and upper North Island and a moderate risk of thunderstorms.
Roads have been closed in Wellsford and the Coromandel due to flooding.
MetService forecaster Tuporo Marsters said up to 66.2mm of rain fell over Pukekohe today and thunderstorms were set to develop in the Auckland region.
"There is an associated moderate risk of localised downpours of 25 to 40mm/hr this afternoon and early evening from Northland to inland Taranaki and northern Manawatu and across to Taupo,'' Metservice said.
"If these downpours occur, they are likely to affect very localised areas.''
The bad weather was forecast to ease significantly tonight.
Rain was also forecast in the Auckland region tomorrow, but was not expected to be as bad as today's downpour.
