Some roads are impassable from flooding and there are reports of entire beaches wiped out from a storm in Coromandel.
A large low-pressure system brought huge waves and strong winds to the east coast of the North Island on Sunday, leading to flooding and road closures.
Civil Defence controller Gary Towler says that's only the beginning - with more bad weather on the way down the North Island's east coast.
"We're just bracing ourselves and I think there'll be quite a considerable amount of damage," he told Newshub.
MetService has issued heavy rain warnings for Gisborne north of the city, with between 70 and 90mm of rain expected between 8pm on Sunday and 11am on Monday.
"Please note, further rain is expected after the warning period ceases, but the hourly rates and rainfall accumulations are forecast to be much less," MetService says.
"Heavy rain may cause streams and rivers to rise rapidly.
"Surface flooding and slips are also possible and driving conditions may be hazardous."
A strong wind warning is also in place for Gisborne north of Ruatoria - with severe gusts of 120km/h expected during Monday.
On Sunday, Thames-Coromandel District Council's Emergency Management and Waikato Regional Council's Flood Room were activated and people are being urged to stay away from the coast.
"We are in for a hammering over the next few days so personal safety is most important," Towler said.
"Huge seas, strong winds, high and king tides over the next few days will likely cause inundation, storm surge, erosion of beaches and damage to the foreshore.
"We have had reports from around the eastern seaboard of huge tides, waves across roads and entire beaches wiped out," he said.
Images from the Coromandel town of Whitianga on Sunday showed State Highway 25, which runs parallel to the sea, covered in water.
