An aggressive front moving across the North Island today is keeping central region emergency services busy with flash flooding.

Fire and Emergency New Zealand spokesman David Meikle said crews had had about a dozen calls for help with flooded buildings and properties this morning.

"They're all related to surface flooding, which has been caused by this heavy rain."

Meikle said the calls were mostly related to commercial properties.

Calls started rolling in about 9am but were dying down by 10.30, he said.

Meanwhile, MetService reported surface flooding at Lyall Bay, on Wellington's waterfront.

"Sudden rainfall after a dry spell runs quickly off the dry ground, and often drains can be blocked with leaves," the service tweeted.

Thanks to Jim Burns for this photo of Lyall Bay in Wellington today. Sudden rainfall after a dry spell runs quickly off the dry ground, and often drains can be blocked with leaves so surface flooding like this is possible. Send your photos in to @MetService ^TA pic.twitter.com/qa1UnmCGmC

— MetService (@MetService) December 25, 2017

MetService had a heavy rain watch in place across Wellington and the Kapiti Coast from this morning until early afternoon.

Similarly, a watch was in place for the ranges of Bay of Plenty east of Murupara, from around lunchtime today.

A brief period of heavy rain and possible thunderstorms were expected as the front moved east across the area. The weather watch could be upgraded to a warning when the wet weather hit.

Metservice meteorologist Tom Adams said things would start to improve behind the front.

"Tomorrow will be a nice day apart from places on the East Coast.

INCOMING!
Front about to reach the North Island. Brief rain, but heavy for some, for all of North Island today. Wellington, Kapiti + Bay of Plenty ranges under a heavy rain watch https://t.co/bcFLKY4OUU ^TA pic.twitter.com/An8WyB82Nc

— MetService (@MetService) December 25, 2017

"On the East Coast the southerly will stick around for quite a few days so there are going to be some strong southerly winds and showers for those eastern parts pretty much through until next weekend unfortunately."

The best place to be today was on the West Coast on the North Island - areas like Milford Sounds and Hokitika.

Weather Watch said the chillier, wet front was expected to turn around for some warmer weather as the week went on. The forecast for New Year's Eve showed a high pressure in the vicinity of the country.

Temperatures looked warm to hot and generally fine, though there was the possibility of some rain on the West Coast and a few isolated showers across New Zealand.