Christmas Day is delivering fine weather and sunshine in the north and promises a clear afternoon for much of the country except the far south.

Aucklanders woke up to a still, clear morning with the good weather not expected to pack up until later today.

Many parts of the country were enjoying a similar fine day interrupted with isolated showers, especially in central and western areas.

"Auckland should be pretty good for most of the day, with long fine spells and a few showers at night," said a MetService spokesman.

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"Wellington should miss most of the wet weather with a few showers and some clouds," he said.

Further south Canterbury was in for a hot day. Temperatures were expected to soar near 30C before the rain arrived later in the day.

However, the rain would continue for southern regions as a frontal system swept up the island.

Adams said the front would stick around the South Island today but would move across the North Island tomorrow, bringing drizzly weather with it.

Fiordland was under a heavy rain warning over the early afternoon and a severe thunderstorm watch was lifted just before 11am.

Southland, West Coast, and Otago were likely to see rain early on as the front moved up the country with rain falling in Canterbury and Marlborough this evening.

Te Anau and Gore were expected to reach just 18C today as the front moved through before lunch.