Dangerous waves are set to hit New Zealand's western coastline on New Year's Day and they may be so high fishers and boaties could be in peril.

Beachgoers are being warned to expect increasing large and powerful swells that will rapidly double in height at North and South Island beaches throughout the day.

Metservice said the dangerous swells will suddenly arrive in sets with the potential to catch those near the water by surprise.

Fishing off rocks and crossing West Coast bars by boat may prove too hazardous for the next couple of days.

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MetService said the waves had been generated from a deep storm in the Southern Ocean and driven by westerly gales roaring across the ocean south of Australia.

The long period waves would begin arriving in New Zealand waters on New Year's Day before rapidly getting larger.

MetService said if you were planning a west coast beach mission it would best to go to a patrolled beach.

Meanwhile the New Year is expected to be ushered in on a fine note for northern and eastern regions but wet in the west.

A front bringing wet weather is expected to stall over the South Island, keeping temperatures balmy in the north.