Kiwis north of Hamilton could be hit with severe thunderstorms and a small tornado as wild weather thrashes the country.

MetService announced a severe thunderstorm watch for Northland, Auckland, Great Barrier Island, the Coromandel Peninsula and Waikato this afternoon.

The warning predicted 120km/h winds or a small tornado, which could damage structures, topple trees, down power lines and affect roads. MetService would update the watch later in the afternoon.

Multiple heavy rain watches cross Te Ika-a-Māui (North Island) for areas including Waitomo, northern parts of Taranaki, Taupō south of Tūrangi, Taumarunui and Taihape.

Residents in the upper North Island should expect a gnarly Sunday afternoon with severe thunderstorms expected. Photo / Supplied

Those near the Gisborne, Bay of Plenty and Whakatāne ranges, as well as the Tararua ranges can also expect heavy rain.

A strong wind watch was also in place for Hawke's Bay south of Hastings, the Tararua District and Wairarapa near Featherston.

Scores of houses and farmland in the upper South Island were completely flooded across Buller and Marlborough - prompting two states of emergency.

Government ministers are in Westport to see the damage.

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Acting Minister for Emergency Management Kris Faafoi announced $300,000 would be offered to the area in the form of a mayoral relief fund, as well as $100,000 for the Blenheim-Marlborough region.

Faafoi said limited rentals for displaced people in Westport continued to be a challenge, and as flood waters receded, welfare issues would become "more apparent".

There were still about 1000 people who were still evacuated in Westport, with about 500 of them who still need welfare support, possibly for weeks and months. Photo / George Heard

About 1000 people were still out of their homes in Westport, and about 500 of them still need welfare support, possibly for weeks and months. Many of them were in Kainga Ora housing.

West Coast-Tasman MP Damien O'Connor said one local farm might have lost 700 animals. Some animals had been moved to places that historically safe, but the Buller River had risen more than it ever had.

He said the river had never been so high, and emergency services had done incredibly well in difficult circumstances to keep the death toll so far to zero.