The public and boaties are being warned to stay out of the water and away from beaches across Hawke's Bay until Wednesday, as the region faces the potential double whammy of tsunami and cyclone after-effects.
The Hawke's Bay Civil Defence Emergency Management Group (HBCDEM) issued the advisory on Sunday after a tsunami surge struck the east coast last night, causing widespread damage in a Northland marina and "unusual currents" and "unpredictable surges" in Hawke's Bay.
The tsunami surge formed after two major events in the Pacific Islands - Cyclone Cody in Fiji and the eruption of underground volcano Hunga-Tonga-Hunga-Ha'pai in Tonga.
HBCDEM group controller Ian Macdonald said the combined impact of the two events meant there was a real safety risk.
"We are advising people to move out of the water, refrain from boating and stay off beaches and shore areas until Wednesday."
He said that included avoiding harbours, rivers and estuaries.
"Cyclone Cody is tracking further to the east then initially forecast and the risk of strong winds and significant rain for Hawke's Bay has reduced, however it is likely that the region's coastline will experience significant waves and hazardous sea conditions from this storm from today through Tuesday."
There is no need to evacuate any residential areas.
"The large volcanic eruption in Tonga has resulted in some minor tsunami activity along the Hawke's Bay coast with strong and unusual currents of up to half a metre in Napier and unpredictable surges observed on tsunami gauges.
"This threat must be regarded as real until the advisory is cancelled."
Macdonald said the Hawke's Bay Harbourmaster recommended boat owners check moorings in the inner harbour.
"Remember, ongoing surges may be larger than others and it is not unusual for tsunami surges to continue for 12 hours.
"Dangerous currents can also persist in harbours for 60 hours or more."
The National Emergency Management Agency (NEMA) has also issued a nationwide advisory recommending people stay out of the water and away from the shoreline in the north and east coast of the North Island, the west coast of the South Island and the Chatham Islands.
"We are urging everyone in Hawke's Bay to keep up-to-date with conditions over the next couple of days," Macdonald said.
Campgrounds and a marina were evacuated overnight in Northland due to a tsunami surge that caused "significant damage" in Tutukaka, on the east coast of Whangarei district.
Boats were "completely destroyed" by a wave around 2m higher than the high tide line - believed to be caused by a combination of Cyclone Cody and the huge volcanic eruption in Tonga.
On Friday, before the eruption, Hawke's Bay surf lifesavers had already suggested people avoid surf beaches for a few days.
Dangerous swells and rips are expected from Sunday through to Tuesday.
Surf Lifesaving NZ search and rescue manager Allan Mundy had said: "If you want to watch the waves go up the hill or stand across the road".
"Just standing on the beach is a risk. If you are caught in that swell you will be pulled right out to sea with little chance of being rescued."
A MetService spokesman said the ocean along the Hawke's Bay coastline would be dangerous, with breaking waves expected to rise to a minimum of four metres.