The 'megathrust' could have 2000 times more energy than the 2011 Christchurch earthquake.

An 8.4 magnitude quake off the East Coast of New Zealand could release 2000 times more energy than the 2011 Christchurch earthquake, experts say.

It could cause a "megathrust" earthquake, and the dangers it poses are being discussed at a summit in Napier this week – with local councils, iwi and civil defence involved.

The potential risk comes from the Hikurangi subduction zone, a massive fault line running from Marlborough and right past the East Coast where the Pacific and Australian tectonic plates collide.

It is potentially the largest source of earthquake and tsunami hazards in New Zealand, but scientists say there is still much to learn about it.

​READ MORE:

* Giant quake risk off east coast of North Island

* Megaquake could hit central New Zealand

* Risk of massive quake under central NZ rises - but still 'very unlikely'

GNS Scientist Dr Laura Wallace told TVNZ "it's a massive plate boundary fault and subduction zones. Because they're so large [they] have the potential to produce the world's largest earthquake and tsunamis".

Marcus Hayes-Jones from Napier Civil Defence said he "can't emphasise how serious" New Zealand must take this "genuine risk".

In 2015, scientists finally found proof that central New Zealand could be ticking down to a highly damaging "megathrust" earthquake.

Previous research has shown the Hikurangi-southern Kermadec subduction zone segment had the characteristics of the locations of previous giant earthquakes.

In 2014, Stuff journalist Michael Daly spoke with the head of that research, Associate Professor Wouter Schellart, of Monash University in Melbourne.

"The southernmost part of the Hikurangi subduction zone is currently experiencing compression," Schellart said at the time.

"The crust in the southern part of the North Island is being shortened and compressed, which implies that the subduction zone fault has high stress on it, which can mean that the fault is temporarily locked."

If that part slipped it could create a large earthquake and potentially could result in a cascading effect, causing segments further to the north to slip as well.

"If a large segment of a fault slips that generates a large earthquake," he said.

In a giant earthquake a very large part of a fault slips.

In the Boxing Day 2004 quake off Sumatra, which caused a tsunami that killed more than 200,000 people, about 1300 kilometres of the subduction zone fault slipped. In the 2011 Japanese quake, about 400km to 500km slipped.

In the Hikurangi subduction zone "numerous" hundreds of kilometres could slip to the northeast, "and then it would be a giant earthquake", Schellart said.

The biggest risk would be between East Cape and Cook Strait, the area immediately bordering the edge of the subduction zone.

Hikurangi is part of a larger subduction zone called the Hikurangi-Kermadec-Tonga subduction zone which stretchs all the way to Tonga.