Hawke's Bay's beaches turned to risky roaring foam pits as the coastline from Napier to Gisborne was hit by a 3m swell on Friday.
MetService meteorologist Kyle Lee said the large swells were being driven by a low pressure system "spinning away" off the East Coast.
"That's driving some strong southeasterlies which is the perfect direction for them to get decent swell."
The high swells impacted large parts of the Bay, north of Napier through to Gisborne, he said.
Lee said waves would reach a peak height of about 3m on Friday, but would be easing by the evening.
"By 6pm on Friday it's coming down to 2.5 metres.
"It's certainly some decent swell."
He didn't anticipate the waves would be "destructive" or cause any major damage, but urged people to be wary of them if around the beach.
A constant stream of people were on Friday morning at Napier's viewing platform to get a good look at the surf.
Kerry Martyn and Sharon Collier from Whangarei, in town to run the Hawke's Bay Marathon, said they had never seen waves like it.
"You do get waves, but this is next level because we don't have the foam," Martyn said.
"It's quite amazing to watch."
Peter Donoghue from Taradale and Lisa Melia from Auckland had also been in town signing Melia up for the marathon when they saw the waves and headed to the viewing platform.
"A lot of the desks are backed up against the windows in the building, a man was talking to me but I was more focused on the waves outside - it's lovely and quite noisy," Melia said.
Henry van Tuel of Coastguard Hawke's Bay said buoys in the harbour had recorded 2.9m swells mid morning Friday.
"Certainly on Marine Parade there's a lot of surf. It's really dangerous along there in particular."
He warned people to stay "well clear" of the water's edge there and be aware of big undertows.
"If you are going out to the sea, make sure it's a sound boat. Over the next day or so, only go if you really have to."
For the surfers eager to make the most of the swell, van Tuel cautioned them not to go alone and to "know your limits".
He expected the surf to return to normal over the next few days.
"It comes and goes pretty quickly."
The tide was at its highest at 7am with a high tide not scheduled until 7.44pm.