What's behind the massive waves being recorded off NZ's coast?

A four-storey monster and a one-in-3000-year giant are among the massive waves detected off New Zealand's coast recently.

So what's happening in Aotearoa's oceans?

Oceanographic service MetOcean measures waves using high-tech buoys. Oceanographer Brett Beamsley told Seven Sharp they work by measuring the "pitch and the roll or the heave" of the ocean as they float along.

Beamsley compared some recent massive waves to "moving office blocks".

He said they "definitely" can get bigger than four storeys, but that wave was "a very good size".

And if a boat encounters a wave like that?

"It's problematic for sure," Beamsley said.

"Most boats will route around those large events, but there is a theory that most of the supertankers or most of the large boats that have disappeared have been due to things like rogue waves, these really, really large waves that occur."

He hopes MetOcean's work can help define design criteria for boats that are going to be operating in the Southern Ocean.

"The modelling's really powerful," he said. "We can also use these to understand the effect of climate change.

"Wave heights on the West Coast of New Zealand are expected to increase with climate change.

"Whereas on the East Coast, they're likely to decrease slightly.

"It is possible that we'll start seeing more and more of those magnitude events hitting New Zealand."