Flood waters have swept through streets and down highways in Auckland, killing four people and damaging thousands of homes, after a deluge of record rainfall.

"It is with the deepest concern that I have been following news of the flooding and severe weather affecting several regions in Aotearoa New Zealand," Charles, who is King of New Zealand, wrote.

"My wife and I send our heartfelt sympathy to the families of those who have lost their lives, and our thoughts are with the many others whose lives have been so terribly impacted by events," he said.

"I have long admired the strength and resourcefulness of New Zealanders, and I send my thoughts and prayers to all those who are supporting response and recovery efforts to help people repair or restore homes, businesses and lives."

He ended with the Maori phrase: "Kia kaha, kia maia, kia manawanui. Be strong, be brave, be steadfast."

Australian Associated Press