Seven districts - including Christchurch, Grey District and Buller District have declared a state of emergency as the cyclone began to make landfall overnight.
Staff have sent out video of the snow drifting down, saying 15cm fell on Tuesday night as the storm lashed central regions, bringing heavy rain to much of the South Island.
'We are expecting homes to be flooded'.
While most of the South Island is out of the woods when it comes to the wild weather, a heavy rain warning remains in place for Dunedin and North Otago.
There are also reports of people being trapped on their roofs by flood waters and one person being swept away, according to the New Zealand Herald.
The Prime Minister of New Zealand, Jacinda Ardern, directed troops to be deployed in areas are expected to be hit the hardest.
'My message still to people is please look out for your local warnings and expect disruption to travel and please just be careful, ' she told reporters at parliament.
Forecasters said Gita would move toward the upper South Island Tuesday evening, and into the southeast on Wednesday.