Wrap up in the winter woollies tonight folks - we're in for a cold night.

People will be waking up to frosty but clear conditions tomorrow morning, with temperatures overnight forecast to drop to 0C and 1C in some parts of the country.

The icy blast follows blustery weather that hit the country yesterday and today, bringing down trees in the capital, as well as delaying public transport.

It is one of the coldest weeks of the year so far. Auckland overnight is supposed to hit 6C, making it the coldest night of the year for the city.

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Christchurch is set to freeze overnight at 0C, while Hamilton is not much better at 1C.

Wellington is forecast to reach 7C, and Dunedin 6C.

While most of the country's main centres will be shaking off the icicles tomorrow morning, the sun should be out in many places, MetService meteorologist Sarah Haddon said.

The sun would be short-lived though, even colder weather is expected to roll in later this week, she said.

Overnight the clouds are expected to clear, which is what brings the temperature down, she said.

"Cloud cover inhibits some of the cooling, the clear skies overnight is the thing that really brings the temperature down."

Despite the clear skies, there will be some "quite strong north westerly winds" bowling through many places.

"That will be something to watch out for."

Weather chaos today forced a Cook Strait ferry to take a seven hour journey to avoid rough seas.

The Bluebridge ferry tried to dodge the worst of the wild weather which last night saw 4-metre swells and southerly winds tipping just under 100km/h whip through the passage.

Strait Shipping spokesman Ed Menzies said in order to make the trip more comfortable for passengers the ship's master took a more southbound course and slowed the vessel which avoided the worst of the swell but meant the journey took seven hours.

The crossing normally takes around three hours.

MetService today issued a fresh weather watch for northwest gales developing over the South Island tomorrow with the possibility of destructive gales in Fiordland, Southland, Otago and parts of Canterbury.

This morning Wellington roads were affected by flooding and a passenger train struck a tree that had fallen on the tracks after wild weather left a trail of havoc across the lower North Island.

The Wellington to Johnsonville line was delayed after an early morning commuter train hit a tree.

All train services on the Melling line were cancelled after strong winds damaged barriers between Petone and Wellington.