Christchurch, Buller, Grey District, Selwyn, Westland, Tasman and Taranaki have each declared a state of emergency as ex-tropical Cyclone Gita shows her heavy hand.
Authorities and people in the affected districts are all on high alert as a state of emergency has been declared in those provinces.
The downpour has also led to record rainfalls particularly in Kaikoura, where 194.4mm had fallen by about 7.40pm - four times more than the monthly normal, according to Niwa.
A total of 53.6mm of rain fell in the area between 4 and 5pm - the wettest hour on record and over a month's worth of rain in only an hour.
"More rain today alone than Nov-Dec-Jan combined,'' Niwa posted on its Twitter page tonight.
The MetService said a "massive'' 255.5mm of rain had been recorded about the Kaikoura ranges from 2am this morning.
"And the rain gauges keep on ticking over for those south of Kapiti. Rain is forecast to ease or clear for everyone by midday [tomorrow].''
With reports of flooding closing roads, trapping people on roofs and at least one report of a woman swept away in Riwaka.
There are heavy rain and strong wind warnings throughout central New Zealand - including in Wellington, Whanganui, Taranaki, Nelson, Buller, Marlborough (including the Kaikoura Coast), Westland and the Canterbury high country.
Gita was poised to split in two when it hit the South Island later today.
The remnants of the storm that battered Samoa, Tonga and southern Fiji was expected to make landfall across the country later in afternoon and night, bringing powerful swells of up to 7m, torrential rain, rapidly rising streams and rivers, slips, flooding and severe gale-force winds gusting to 150kmh in places.
Gita has been downgraded to a storm, but forecasters warned it was still likely to wreak havoc as it traversed the centre of the country, the West Coast and Canterbury.
It may now be divided by the Southern Alps - sending the main storm over Banks Peninsula and a second, smaller storm towards the West Coast, the MetService warned this afernoon.
Latest forecasts show Canberbury was set for heavy rain and high winds, with potentially serious impacts. Banks Peninsula was expected to bear the brunt of the storm.
The declaration highlighted the severity of the potential impacts of the weather, and gives people early warning to prepare, the Christchurch City Council said.
“The full impact of the storm will be felt overnight and tomorrow morning. We are expecting homes to be flooded. If you are in a flood-prone area, particularly if your home was flooded, or close to flooding, in the July storm last year, you should consider evacuation before the worst of the storm hits tonight,” Dalziel said.
Meanwhile, Prime Minister Jacinda Ardern said the military has been deployed to areas likely to be worst hit by Gita and the country's national Civil Defence office in Wellington was on standby to help local authorities.
"My message still to people is please look out for your local warnings and expect disruption to travel and please just be careful," she said today.
Air New Zealand said flights at Queenstown, Hokitika, New Plymouth and New Plymouth have been cancelled, flights at Nelson cancelled from midday, and flights at Wellington airport would be cancelled between 2.45pm and midnight.
This may have a flow-on effect to other services as former Cyclone Gita approaches and weather conditions are forecast to deteriorate.
Flights are currently operating into and out of Blenheim, Kapiti Coast and Palmerston North, the airline is closely monitoring conditions there.
KiwiRail’s TranzAlpine service had been cancelled for Tuesday and Wednesday due to the severe weather expected, affecting about 1400 passengers. A rail charter service between Christchurch and Arthur’s Pass had also been cancelled.
At this stage no Interislander sailings have been cancelled, but general manager Mark Thompson said they were carefully monitoring the weather and cancellations were possible.
The Department of Conservation was closing picturesque seaside hiking tracks and campsites along the West Coast and ushering tourists away from low-lying areas.
"Due to heavy rain SH1, north and south of Kaikoura, has now closed. Travellers heading to and from Picton should use the alternate route via the Lewis Pass," the New Zealand Transport Agency said this morning.
With steady rain falling along the Kaikoura coastline, NZTA closed the main highway on both sides of the town, Mangamaunu to Clarence and Peketa to Goose Bay, just after 8.30am. There have been some minor rockfalls on the Hundalees south of Oaro and also along the coast.
Route 70, the inland road via Waiau remained open for road access to Kaikoura. While crews would aim to keep it open as long as possible, drivers were urged to delay all but essential trips in the area until the severe weather has passed.
All drivers travelling from Picton to Christchurch were advised to take the Lewis Pass route via Waipara and St Arnaud.
Authorities in the Marlborough Sounds have told campers to abandon their positions to be safe. People are being advised to secure property and items that may be blown away. Pets should be kept inside for their safety.
For the North Island, coastal areas from Raglan to southern Wairarapa were most at risk, while for the South Island Buller, Nelson and the Marlborough Sounds and Banks Peninsula were expected to be among the worst hit, MetService said.
Heavy rain warnings were in place for Nelson, Buller, Marlborough (including Kaikoura Coast), Wellington, Westland, the Canterbury Plains, the Canterbury high country and North Otago.
Strong wind warnings were in place for Taranaki, Taihape, Whanganui, Nelson and Buller, Marlborough, Westland, Fiordland and Canterbury.
- Additional reporting NZME
The Department of Conservation was closing picturesque seaside hiking tracks and campsites along the West Coast and ushering tourists away from low-lying areas.
