Air New Zealand says it will have extra flights on Thursday to clear the backlog of travellers stranded at fog-covered Wellington Airport.
Wellington was packed to bursting point with no hotel accommodation left in the city after aeroplane passengers were left stranded at the city's airport.
More than 100 flights have been affected by a thick layer of fog in the capital city on Wednesday, causing cancellations of arriving and departing flights.
The airport handed out blankets to passengers left stranded.
Cancellations continued overnight, with all flights remaining suspended until the fog clears.
Domestic and international flights into Wellington have been diverted to other airports or turned back to their origin.
The fog arrived early on Wednesday morning, and is expected to clear during the day on Thursday.
Travellers should check their flight status with their airline or on Wellington Airport's website.
Bad weather is rolling across the country, sparking severe weather watches for parts of the North Island.
Auckland Civil Defence says it's monitoring the situation as it expects to be hit hard by heavy rain along with the Coromandel, Bay of Plenty and Waikato.
MetService's Tuporo Marsters says the downpours will be affecting localised areas.
"Rainfall of this intensity can cause surface and flash flooding in low-lying areas and may lead to slips" he says.
"It's quite a soggy situation."
Mr Marsters says he is hopeful the rain will ease this evening.
The New Zealand Transport Agency is warning drivers to be careful of slips on State Highway 25, from Tararua to the Coromandel.
Mr Marsters says Wellington is "a steam room" and the air is saturated, with moist air that came in with a southeasterly late on Wednesday morning.
The hill suburbs of Kelburn, Newlands, Maungaraki, Mt Victoria, Roseneath and Johnsonville are blanketed in thick fog.
Fog is defined as visibility being less than 100 metres.
The temperature in Wellington is 15degC, and the dew point is also 15degC - the point at which condensation occurs.
Motorists should watch their following distance if they are venturing out into the fog, Mr Marsters says.
There have been minor crashes and traffic delays in Wellington on Wednesday morning. NZTA Wellington says traffic has now returned to normal volumes.