Several tourists are seeking emergency accommodation in Haast.
• For overnight updates on Cyclone Gita - stay tuned to Newstalk ZB
Christchurch, Buller, Grey District, Selwyn, Westland, Tasman and Taranaki have each declared a state of emergency.
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.
There is also a road snowfall warning in place over Lindis Pass, Crown Range Rd, and some flights have been affected due to bad weather conditions. There are also many reports of flooding.
Just before 7pm, authorities said Route 70 Inland Road to Kaikoura had been closed off completely.
The highest wind gusts recorded in the last 24 hours were in Hawera where 130km/h north-westerly winds were recorded, while 118km/h easterly winds were recorded in Westport.
The MetService warned that winds of that strength can bring down trees and send unsecured items flying.
There was some good news, however, as winds are expected to easy by tomorrow morning.
Weather experts say the former tropical cyclone - which ripped through Samoa and then Tonga last week - may be divided by the Southern Alps; sending it over Banks Peninsula and then towards the West Coast.
Just before 6.30pm, MetService said the cyclone system had created large northwest swells over the Western Coasts, from Buller to Northland.
"Port Taranaki just measured max waves of 6.7m," the MetService said.
"This heavy swell plus onshore winds plus high tides equals possible coastal inundation."
People in those areas were encouraged to keep up to date with weather reports and messages from authorities.
A Fire and Emergency spokesman said just after 7.30pm that crews were "flat-out'' tonight, attending to call-outs from all over the affected regions.
Most of the jobs they were being called out to involved rooves being lifted off homes and buildings, powerlines down, trees across roads and homes and businesses being flooded.
Many of the call-outs were in Taranaki, the Tasman District and on the West Coast.
Fire crews had also been called to a number of landslides, including that in Takaka, where a main road had since been completely closed off.
Staff were being told that the weather system was now moving towards the Manawatu and as a result, the Fire Service had started to get calls from people in those areas, including in Palmerston North, Whanganui, Levin and Foxton.
A dedicated media line would remain open throughout the night to give updated information on the situation.
Meanwhile, some schools in the worst-hit areas have already indicated they will be closed tomorrow.
The Ministry of Education advised parents to keep in contact with their child's school or early childhood education centres to understand whether or not they would be open this week.
It said it was supporting the following schools.
A press release said the ministry had been advised that all schools and childcare centres in the Buller District would be closed tomorrow. The same goes for schools in the Grey District.
Parents were told to keep an eye on their respective school's website or Facebook page for direction.
"Today, 90 schools and 98 ECE services in Nelson, Marlborough, West Coast, Canterbury, Wellington and Taranaki regions closed - impacting more than 20,000 students and pre-schoolers.
"We are providing support where needed and our support will be available for as long as it's required.''
