A heavy blanket of fog over Auckland is affecting flights and motorways but also keeping winter temperatures at bay.

At Auckland Airport, 28 domestic flights have been cancelled and 19 delayed because of the fog.

Fog restrictions were put in place about 4am this morning and were lifted at 9.05am.

Affected flights include one to Wellington cancelled, and eight delayed to Christchurch and Queenstown.

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MetService lead meteorologist Mark Todd said the fog stretched from Auckland through Waikato, Waitomo and Taumarunui.

"It set in overnight, but in Auckland it was more early morning. Auckland can be very stubborn with fog, so the best indication is it could be around until midday."

The NZ Transport Agency has also warned of heavy patches of fog on the Southern and Northwestern Motorways.

Once the fog cleared, however, it should be a fine day for Auckland, with light southerlies and a high of 13C.

Central parts of the country continued the cold spell, with temperatures at about 5.30am dropping well into the negatives.

In the South Island, Tekapo was at -4C and Pukaki -5C, while the central North Island was sitting around -2C.

Most of the country would clear for a fine day, Todd said.

Northland could start the day with a few showers, but these would be gone early afternoon.

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The only other areas with a bit of unsettled weather were the North Island's East Coast, which would get a few isolated showers from Gisborne to Wairarapa, and the far south around Southland and Clutha.

Tomorrow was looking like the best day of the weekend, Todd said.

"It will start off fairly cool again, but should warm up across the country."

The ridge of high pressure covering the country was expected to slowly move east on Saturday, as a front approached from the Tasman Sea.

The effects of the front, arriving Sunday, would start to affect the West Coast of the South Island and lower North Island late Saturday.

On Sunday periods of rain were forecast for many places, including potentially heavy rain about Westland, Buller and northwest Nelson, Taranaki and the Tararua Range.

A showery west to southwest flow would follow on Monday, when westerly gales were possible about the lower North Island.

A ridge was forecast to spread over much of the country on Tuesday, easing the southwesterlies and showers for most places.

However, the showers would persist about Northland, as the winds tended easterly there.

Today's weather

Whangārei

Fine, but chance shower until afternoon. Southerlies. 15C high, 4C overnight.

Auckland

​ Foggy start then becoming fine. Light southerlies. 13C high, 3C overnight.

Hamilton

Fine, apart from morning fog. Light winds. 13C high, -2C overnight.

Tauranga

A fine day. Light winds. 15C high, 3C overnight.

New Plymouth Fine, but cloud at times. Light winds. 13C high, 2C overnight.

Napier Fine, but cloud at times. Some morning frosts. Light winds. 14C high, 0C overnight.

Wellington Partly cloudy and the chance of a morning shower. Light southerlies. 12C high, 5C overnight.

Nelson A fine day with morning frosts. Light winds. 12C high, 1C overnight.

Christchurch Morning cloud and early frosts, then fine. Southwesterlies dying out in the morning. 12C high, -1C overnight.

Dunedin Morning cloud breaking to long fine spells. Light winds. 11C high, 4C overnight.