Prime Minister Bill English on a visit to flood-hit Edgecumbe says residents will need ongoing support for some time.
"There's 900 empty households, and some proportion of them..no-one will ever go back," he says.
There needed to be a full investigation into the flooding, he said.
Almost the entire town of 1600 people was evacuated after the Rangitāiki River burst its banks, and nearby communities have been cut off by slips and high water.
Floodwaters surged through the town after days of heavy rain that caused flooding, slips, power cuts and road closures across the North Island and affected parts of Canterbury, including earthquake-hit Kaikōura.
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