The massive downpours that have turned much of New Zealand into a sodden landscape of swollen rivers, wrecked homes and flooding will be no easy chore to clean up, emergency officials say.

A state of emergency in parts of the flood-battered South Island will remain in effect as authorities survey the damage in the region hardest hit by four days of torrential rain.

Last week’s rains in northern and central areas forced more than 500 people from their homes, leaving some uninhabitable.

The South Island city of Nelson has been worst affected, but towns in the North Island have also been cut off by floods that have swamped roads and homes.

‘Working as quickly as we can’

Authorities in the region around Nelson said there had been no further serious weather incidents or evacuations overnight on Saturday into Sunday.

“We are working as quickly as we can to get people home safely,” emergency management officials said, adding that while they had looked at about half the affected properties, detailed inspections could take days and would depend on ongoing weather conditions.

“We have a big task, and inspecting for land instability is more complex than for flooding.”

While the extreme weather has eased, warnings against heavy rain remain in western Tasman and Fiordland on the South Island, forecaster Metservice said on its website.

A state of emergency continues in the regions of Marlborough, West Coast and Nelson-Tasman, national emergency officials said.

“Listen to local authorities and follow any instructions to evacuate,” the agency said on its website.

“If you feel unsafe, you should self-evacuate.”

On Saturday, Kieran McAnulty, the emergency management minister, thanked rescuers but added that recovery was likely to be a “long and difficult” process.

-with AAP