Residents near Twizel were treated to an icy phenomenon known as a hoar frost this morning.
MetService meteorologist John Law said the hoar frost forms in a combination of low temperatures and moist air.
"Moisture can freeze onto really cold surfaces, creating these delicate bits of ice."
MetService said if the air temperature of a fog is below 0°C, frost crystals can gradually grow via deposition into a thick coating on trees and bushes.
"The resulting frozen lace work is called a hoar frost."
These frosts are distinctive due to its hair-like or feathery structure, and the freezing process is so fast that it traps air.
"Small air bubbles trapped in the ice are the cause of the crystal's white colour," MetService said.
The word "hoar" comes from Old English and means "grey with age". It gives its name to the frost because the way the ice crystals form make it look like white hair or a beard.
Hoar frosts can occur across New Zealand, but are prevalent in your "classic" cold spots, Law said.
"Those lingering areas of mist and fog, so places like Wānaka and Twizel where you find the valleys filled with mist and fog through the night.
"You can just imagine that the whole frosting can grow, with frosts forming on frosts which can help develop those features."
He said there could still be pockets of frost and cooler temperatures for inland areas in the coming week.
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