People living by the sea in affected communities are urged to take care around roads, particularly on the west coast of the North Island and the top of the South Island.
MetService forecaster Mmathapelo Makgabutlane said a heavy swell alert had been issued for western regions of both islands.
The waves would start rising at the bottom of the North Island between Otaki and Waitotara from tonight and not ease off until tomorrow afternoon.
She said at their maximum height they would reach 5m tomorrow morning.
Further north along the Taranaki coast between Mokau and Opunake the waves would hit later tonight and rise up to 5m in the morning for a spell. The waves were not expected to ease until Sunday.
Makgabutlane said the mountainous waves were a combination of swells and wind effects.
"We've got very strong winds starting from today already across the North Island and parts of the South Island so that is generating very wind-driven waves," she said.
The latest weather alert now has the entire North Island under a strong wind watch, with Taranaki and Wellington at warning levels. Damaging gales of up to 140km/h are forecast to barrel through the regions and not expected to ease off until tomorrow evening.
Parts of Bay of Plenty and Taranaki sit under a rain warning, with up to 120mm of rain expected to fall across the weekend.
MetService is warning heavy falls may lead to flooding and slips, with driving in the areas hazardous for motorists.
A rare rain red alert sits over Buller and Westland north of Fox Glacier on the West coast, with surrounding regions under warnings and watches.
Thunderstorms are expected to lash the region, with up to 400mm of rain expected in total across the weekend.
People are being warned the deluge is likely to lead to significant flooding which threatens to cut off communities and lead to dangerous river conditions.
There are also road snowfall warnings for two alpine passes this weekend, with up to 1cm expected to settle on the summit routes.
