The National Institute of Water and Atmospheric Research says this January could be one of the coldest on record.
Some parts of New Zealand, including Wellington and the Canterbury coast, have experienced maximum temperatures of around 12 degrees in the past three days.
NIWA says that's 10 or more degrees below what is normally expected at this time of year.
Climate scientist Dr James Renwick says temperatures in much of New Zealand are more than one degree, and in some places more than two degrees, below normal to date this month.
He says that's remarkable and New Zealand could be set for a record cool January if low temperatures continue for the rest of month.