Extra services will be put on and a larger aircraft is being brought in, to deal with a massive backlog of travellers at Wellington Airport.
More than 100 flights have been cancnelled tonight and tomorrow morning, due to fog and low cloud which isn't expected to clear until mid-morning tomorrow.
Flight QF 163 from Sydney may be allowed to land if weather permits, and check-in has been suspended for flight flight SQ292 to Canberra.
Air New Zealand said normal flights will resume at 9am, a Boeing 777-200 aircraft will fly busy routes, and six extra Airbus A320 services will fly between the main centres.
The airline said it's working with customers to arrange alternate flights, transfer their booking to another day, or hold the fare value.
"Weather conditions at Wellington Airport have caused significant disruption to flight operations throughout today with services unable to land or depart since mid-morning. The suspension of services has caused flow on effects to other services.
"Air New Zealand will also operate a number of extra Airbus A320 services tomorrow to accommodate disrupted customers, in addition to the 777-200 aircraft which normally operates on international routes.
Wellington Airport said people who have been delayed at the airport for an indefinite time have been offered free bottled water by the airport.
Travellers who need to stay overnight will be provided with complimentary blankets, water and snacks.
The airport is asking travelles to check their flight status through their airline or the Wellington Airport website.
"Fog and low cloud is also currently forecast in the Wellington area for tomorrow morning, Thursday 30 March. The airline will continue to monitor weather conditions on the ground and will look to resume operations tomorrow as soon as possible," they said.
Air New Zealand is advising customers to consult the arrivals and departures information on the Air New Zealand website for up to date schedule information.
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.
Drivers caught by rising floodwaters have had to ditch their vehicles after becoming trapped in Auckland as wild weather batters the country.
A severe thunderstorm watch has been issued by the MetService for much of the North Island - Northland, Auckland, Waikato, Waitomo, Taumarunui, Taupo, Taranaki, Taihape, Wanganui and Manawatu.
The watch is 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.
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 this afternoon.
"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 is forecast to ease back significantly tonight.
Rain is also forecast in the Auckland region tomorrow, but is not expected to be as bad as today's downpour.
Flights have been suspended to and from Wellington due to sea fog, which has also severely reduced visibility on the region's roads.
Roads have also been closed in Wellsford and the Coromandel due to flooding.
In Auckland, heavy rain this morning caused flooding in Ramarama, Pukekohe and Papakura.
Fire Service northern shift communications manager Colin Underdown said a motorist became stranded by a flash flood on Foy Rd in Pukekohe.
The alarm was raised about 11.40am by roading contractors who spotted the driver in trouble.
However, the driver managed to make his way out on his own.
"The person headed out through the water on foot," Underdown said.
The man's vehicle was hauled out by a tractor owned by a local grower.
Nearby, on Maxted Rd on Ramarama, a postman became trapped in his delivery van and had to be towed by a local in his truck.
Fire crews were called to pump water from a number of flats in Victoria St, Pukekohe, and a garage in Seddon St, which became inundated by floodwaters.
A large culvert burst its banks in Goodwood Heights, Manukau, and extensively flooded a home in Flamingo Court.
Vegetable grower Kiran Hari of Pukekohe said the deluge was likely to affect his crops.
"There's water everywhere. It's just a lot of water in a short space of time,'' he said.
"There's going to be some crop losses. Some of the young planted stuff - that's under water.''
Auckland Transport said contractors were at Subway Rd in Pukekohe, which was closed between Manukau Rd and Station Rd, and at Ponga Rd in Papakura.
A major road near State Highway 1 in Wellsford was also closed this morning because of flooding.
Wayby Station Rd, Wellsford is CLOSED due to flooding. Take extra care in the area and avoid unnecessary travel. ^LC
— Auckland Transport (@AklTransport) March 28, 2017
All services have been suspended at Wellington Airport this morning #LiveCam
Posted by nzherald.co.nz on Tuesday, 28 March 2017
Thick fog rolled in to Wellington overnight, grounding all flights.
An airport representative said they managed to get some flights airborne this morning when the weather cleared momentarily.
But the fog rolled back in, putting a halt to operations.
The airport says anyone needing to catch a flight should keep an eye on the website for the most up-to-date information.
Flights were also cancelled and diverted away from the capital last night because of fog.
The fog situation is expected to improve mid-afternoon, Air New Zealand says.
"The airline is continuing to monitor weather conditions on the ground. The situation is expected to improve mid-afternoon and operations will resume as soon as possible," a spokesman said.
Air New Zealand is advising customers booked to travel to and from Wellington to consult the airline's website for up-to-date information.
"Customers who no longer require 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 our contact centre today."
Air New Zealand will help customers reschedule.
"We recommend customers ensure they are subscribed to Air New Zealand's Travel Alert service to receive updates."
Greg Bruce was on a flight from Auckland to Wellington at 9am but was turned back because of the fog.
Bruce, who was heading to Wellington for work, said the plane got to Wellington but was unable to land, and was sent back to Auckland.
He had a return flight booked for later in the day as well, and received a notification it had also been cancelled.
He and other passengers were told ground staff would meet them in Auckland to help them make other arrangements, but nobody met the plane.
"So good work, Air New Zealand," he said.
"People were clearly put out. But yeah, it's just one of those things, isn't it? It's just an inconvenience, isn't it?"
Bruce said there was nothing anyone could do about it.
.
#TakeCare out there due to reduced visibility. Remember your following distance and switch on to be seen. ^MN pic.twitter.com/SXKUwkv23f
— Waka Kotahi Wellington (@WakaKotahiWgtn) March 28, 2017
"Everything's going to be fine, we're all going to survive."
Police say this morning's foggy, misty conditions also led to a spate of road crashes across the region, causing major traffic delays for commuters.
Thick fog is hampering travel on the city's roads and transport authorities are pleading for motorists to turn on lights and keep big following distances.
A number of crashes at rush hour on the capital's motorways led to long queues at Pukerua Bay, Johnsonville, and south of the Mungavin Ave ramps.
⚠ ✈️ All flights suspended due to fog at WLG Airport. Please check our website for any updates: https://t.co/M7HtbkdVVu pic.twitter.com/ExF2Kerto9
— Wellington Airport (@WLGAirport) March 28, 2017
MetService meteorologist Lisa Murray said the moisture-laden active low would track south along the eastern side of the country today pushing low cloud over skies and the possibility of sea fog in coastal areas.
"At the end of the day it's all the same, we're in cloud. You can't see anything, it's sort of damp. That's just the type of weather that it kind of is."
The low was expected to bring a lot of rain from Auckland, Coromandel, Bay of Plenty to Wairarapa, although temperatures would remain in the balmy 20s, thanks to the warm humid air.
Murray said it looked as though the fog would be around for most of the day, and although it might clear in the afternoon, it would "come in again thick and fast in the evening".
"You won't be sunbathing too much today, it's not one of those days."
A severe thunderstorm watch was also issued this morning for the upper North Island to northern Manawatu, and threatening weather is likely until evening.
Severe Thunderstorm Watch issued https://t.co/XStUElvTQB pic.twitter.com/5HR62u19AL
— Severe Weather Info (@MetServiceWARN) March 28, 2017
Murray said rain would be particularly heavy in the Gisborne region.
Heavy overnight rain had left parts of the Coromandel under water after the Manaia River breached its banks across State Highway 25, and patches of surface flooding in Coromandel Town.
Slips had also come across the highway north of Thames.
Stop-go traffice management on SH25 just north of Thames and flooding on SH25 at Manaia are the only road closure... https://t.co/GMxZ8tJRZD
— ThamesCoromandelDC (@OurCoromandel) March 28, 2017
It comes after heavy falls drenched suburbs across South Auckland yesterday. An overnight deluge gave the suburb of Mangere its wettest March on record with the total monthly rainfall nearly three times above normal.
With 239 mm of rain through 8:00 am, #Auckland (Mangere) has recorded its wettest March on record. Monthly rainfall 281% of normal! #climate pic.twitter.com/BVu8AXQaET
— NIWA Weather (@NiwaWeather) March 28, 2017
Showers were forecast for the lower half of the island this morning.
Murray said it would be a generally fine day across the western half of the South Island but clouds would likely cover the eastern side.
Kaikoura would be shrouded in cloud and sea fog today.
CRASH: #SH1 Porirua blocking the right southbound lane north of Mungavin Interchange. Please use the left lane and #ExpectDelays ^MN pic.twitter.com/YMBsAx9enl
— Waka Kotahi Wellington (@WakaKotahiWgtn) March 28, 2017
Motorists were asked to drive with care and patience in what are foggy and misty conditions in some areas.
Meanwhile, as ex-tropical cyclone Debbie tracks over inland eastern Queensland forecasters are watching its path to see what will happen when it moves back offshore later this week.
Two of three tracking models have the storm heading offshore from Brisbane on Friday and weakening.
One UK global model has the system moving into the Tasman Sea, re-energising over open waters before moving close to New Zealand on Sunday.
Auckland: Morning rain, showers, thunder. 24C
Hamilton: Morning rain showers, thunder. 23C
Wellington: Drizzle, morning fog. 18C
Christchurch: Cloudy becoming fine. 19C
Dunedin: Fine. 19C
Firefighters are keeping a close watch to ensure the piles of debris do not reignite.