"I want to be really clear it's not an expectation, it's a concern I constantly hold, we're talking about a massive unprecedented weather event," McAnulty said.
McAnulty said about 10,500 people had been displaced by the storm, while 144,000 were without power.
The New Zealand Defence Force (NZDF) said it had rescued hundreds of people from the Hawke's Bay alone, including by winching people off roofs of houses.
New Zealand police said there had been 1,442 reports made of uncontactable people, most from the eastern regions of the North Island