SYDNEY - A clean-up began in New Zealand's capital Wellington after flash flooding, ​sparked by heavy rain, hit the nation's ‌North Island, authorities said on Sunday.

"Severe weather has caused flood damage across the city," said ​Hutt City Council, a government authority ​within the Wellington region, which has ⁠a population of 520,971.

"We know many people ​across Lower Hutt are dealing with flooding ​impacts and debris," the council said, adding that crews were in the field cleaning up "hardest hit ​areas" in the suburb of Stokes Valley.

A ​state of emergency was declared in the Whanganui District ‌150 ⁠km (95 miles) north, and 18 people were evacuated due to flooding, public broadcaster Radio New Zealand reported.

The nation's weather forecaster ​predicted more ​thunderstorms, accompanied ⁠by very heavy rain, for parts of the North Island ​including Wellington on Sunday.

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"These severe thunderstorms ​are ⁠moving towards the southeast," it said.

The wild weather, which sparked evacuations on Saturday, follows the ⁠island's ​battering a week earlier ​by Cyclone Vaianu, which forced residents to higher ground.