Transpower says Sunday's cold snap caused electricity usage to spike 5% - 10% higher than Sunday a week ago.
According to MetService, warm summer temperatures were interrupted on Sunday by a southerly front that dragged cold air from the Antarctic over the length of the country.
Snow was reported in the Southern Alps and through Porters Pass, down to about 1200 metres above sea level.
Temperatures dropped dramatically in the lower North Island, including in Masterton, where the mercury fell from 21 degrees to 11.
Hiowever, summer conditions should return on Monday.