New Zealand wakes up to a frosty morning

New Zealand has woken up to a frosty morning as winter truly begins to bite.

Only one part of New Zealand had zero risk of frost overnight, forecaster NIWA Weather wrote on Twitter.

It shared a map of New Zealand showing Northland through to Southland dotted with spots or high or low frost risk.

The Chatham Islands were the only part of the country not affected.

It's epecially freezing down south this morning, MetService says. Temperatures as low as -7C have been recorded at Pukaki Airport and Mt Cook, while St Araud and Omarama got down to -6C.  

NIWA Weather spokesperson Chris Brandolino warned on Tuesday that Wednesday morning was expected to be the coldest of the year so far.

MetService says Auckland was expected to hit 5C overnight, while Christchurch dropped to -2C and Queenstown was forecast to drop to -3C.

Brandolino told The AM Show on Tuesday the cold temperatures are being driven by the upcoming Winter Solstice, or the longest night of the year, which will happen on June 22.

"Recipe for a very cold morning: You want long nights, we pretty much have that, the longest night of the year are approaching the solstice.

"[You need a] cold air mass, this is coming from deep in the south, dry air mass, and we have light wind, high pressure.

"The only thing we are missing from the critical cold list is a fresh snow pack."