It's very wet, and it's going to stay wet, MetService says.

Heavy rain that has plagued the North Island today is set to continue tomorrow while the South Island can expect heavier rain than it's been experiencing, meteorologist April Clark says.

"Essentially this wet weather is set to last for most places into tomorrow," she says.

The area experiencing the most rain over the last 12 hours was the North Island's Coromandel Ranges which have collected 57.8mm of rain since 2am.

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In more populated areas, Northland's Kerikeri and Kaikohe had 39.2mm and 38.8mm of rain respectively.

"That's really persistent rain that hasn't let up," Clark says.

While the rain had been steady across most of the North Island today it would be more "on and off" for the afternoon and evening but the wet would continue into tomorrow.

However the hammering would intensify in the South Island, where a heavy rain warning is in place for Nelson, Richmond Ranges, Buller, Westland and north of Franz Joseph.

The deluge comes after the west coast of the South Island was recovering from ex-Cyclone Fehi last week, which caused power outages and prompted a declaration of a state of emergency in Buller.

In the meantime New Zealand was safe from Cyclone Gita, which has been upgraded to a category two cyclone and is expected to reach category 3 - meaning severe- in the next day.

Gita battered Samoa overnight, causing widespread flooding, and is heading towards Niue and Tonga.

It was likely to stay in the tropics for at least a few days and wasn't likely to affect New Zealand at this point, Clark said.

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WeatherWatch.co.nz said it was "far too early" to be able to tell if it would reach these shores and forecasters would be watching it over the next few days before warning New Zealanders about its possible impact.