Weather: Sub-zero temperatures to spread across South Island on Sunday

Sub-zero temperatures will see the South Island shivering on Sunday morning as cold air brings an icy start to the day.

The freezing nights will hit hardest around the mountains, NIWA says, and could be dangerous if you're outdoors.

"Heads up if you'll be camping or tramping across the South Island high country or higher elevations this weekend," NIWA warns.

"Note the chances for temperatures to go below 0C Saturday and Sunday morning."

A NIWA graphic shows a high chance of below-freezing weather running along the Southern Alps.

And much of the South Island will also see a cold start with temperatures dipping into the low single-digits.

Wanaka, Queenstown and Alexandra will see a low of around 4C early on Sunday morning, and could even be in for a spotty frost, NIWA says.

"You'll need a heavy jumper waking up on Sunday morning but a T-shirt by the afternoon as temperatures will be around 21C or 22C," NIWA scientist Christ Brandolino told Newshub.