The South Island can expect temperatures as low as -15 this weekend.
A strong high pressure system, combined with clear skies and long nights mean temperatures could drop as low as -15 degrees.
"These are going to be unusually high sea-level pressures, that means the air is being pushed down from above, high pressure makes the air sing," NIWA meteorologist Chris Brandolino told Morning Report.
Brandolino said he doesn't know if they'll be record-breaking temperatures like the fourth coldest temperature of all time, -21 degrees in June 2015, but it may get as cold.
"There will be some pretty cold air across New Zealand."
The long nights will help to facilitate the cold temperatures, he said.
With cold temperatures comes a risk of black ice and Brandolino says people need to take particular care when driving on back roads and country roads.
The temperatures are good news for some, the Mt Hutt ski field opens this weekend.
"This will certainly help ski resorts especially, those who haven't been dealing well because mother nature hasn't been playing ball."
For those keen to head out on a winter tramp, Brandolino said it's important to take extra care.
"You really have to keep in mind the risks for hypothermia, temperatures -10, -15, that's really cold stuff and it doesn't take a long time of exposure to really start to feel the negative impact, you really want to dress appropriately."