Earlier in the day it issued a grid emergency notice and said it was removing some transmission lines from service across the South Island as a precaution.
The grid emergency now affects transmission throughout the country.
An "extreme" geomagnetic storm is affecting Earth at present.
Material fired out from a sun spot is crashing into the planet's atmosphere this weekend.
The storm has the potential to disrupt power and satellites, as well as communications and GPS.
The US Space Weather Prediction Centre says G5 (extreme) geomagnetic storms can impact power grids, satellites, and radio communications.
The increased geomagnetic activity brought stunning Auroras to much of the country last night, and is expected to do the same again tonight.
MetService meteorologist Clare O’Connor told the New Zealand Herald hopeful watchers may be able to view the aurora again tonight, with little to no cloud cover expected for much of the North and South Islands.
"Unfortunately for the very deep south, like Invercargill, it might be a bit cloudier. Dunedin will hopefully escape the cloud, the other exception is Marlborough Sounds/Blenheim with it being a bit cloudier around there."
"What's happening is that material from the Sun is crossing space and interacting with earth's magnetic field generating electric currents all over the place and that's potentially doing things like interfering with the power grid and also causing amazing auroras.
"Obviously for folks like myself who like watching auroras it's a very exciting time."
The solar storm is expected to peak tonight, with the US Space Weather Prediction Centre forecasting severe conditions from 6-9pm (NZ time) on Saturday.
NIWA says although most solar events do not cause much impact, this is an "unusually strong event" so it pays to be prepared.It recommends people ensure they have charged batteries and flashlights in case the power goes out.
The warnings comes after another freezing start to the day for some parts of the country with temperatures dropping as low as -6 degrees Celsius.
MetService said a high pressure system was moving into New Zealand from the southwest, bringing with it frosty temperatures.
Mt Hutt saw a low of -6C, while Mt Cook and Alexandra dropped to -4C.
Meanwhile, in the North Island Taupo was -2C.
Transpower, the national grid operator has issued a grid emergency notice this morning and is removing some transmission lines from service.
However, power supply is not at risk, it says.
MetService says colder temperatures are expected to persist for the next few days, before warming slightly early next week.
The cold snap has been in place for a few days with Christchurch registering -6C on Friday and Mosgiel at -5.3C on Thursday.
The national grid operator Transpower asked households and businesses to conserve electricity on Friday morning due to the cold snap, coupled with several power plants undergoing maintenance.
There were fears that Transpower would have to work with lines companies to control the load and even switch off supply, but that did not eventuate.
Tonight is also forecast to drop back below freezing in central areas, MetService meteorologist John Law said.
"More cloud in towards Whanganui down towards Manawatū and Wellington and I think as we head through the morning, that should start to break up and clear away."
It will turn into a fine clear night but a pretty cool one as we head into Sunday morning, he said.
On Sunday the North Island will reach highs of 15C in Auckland, with Tauranga looking like the spot to be with plenty of sunshine reaching 16C.
The South Island is looking fine and dry through the daytime on Sunday but there is more cloud for the southern parts of Otago and an odd shower for Southland and Fiordland Coast, Law said.
- Additional reporting ODT Online
