UPDATED 6.44pm The Prime Minister says the damage to the Kaikoura region is worse than he thought.

LISTEN ABOVE: John Key and Gerry Brownlee speak to Larry Williams after being in Kaikoura to inspect the quake damage

John Key inspected earthquake damage around Kaikoura and Marlborough with Gerry Brownlee, Opposition leader Andrew Little and a small group of journalists on an Air Force NH90 helicopter.

VIDEO (NZNats / Youtube)

Massive slips could be seen as he flew over in a Defence Force NH90.

"It's just utter devastation, I just don't know...that's months of work," John Key told Gerry Brownlee and pilots.

"The slips here are horrendous and you've got to believe it's in the billions of dollars to resolve these issues. They're huge slips."

He hoped there were no cars stuck underneath the heavy rockfall.

"It's lucky it was midnight".

He said it's worse than the Manawatu gorge slips.

Key and Brownlee estimated the clean up will run into the hundreds of millions and clearing the debris and blocked roads could take months.

As the chopper surveyed damage over the wider Kaikoura area, further earthquakes hit and dust from rockfalls and slips could be seen.

"That's a goodie", one of the pilots commented as the quake hit.

Dust billowed down the hillside as the chopper circulated. The pilot said he'd never been airborne when a quake had hit before.

Key asked how big the quake was but the pilot didn't know.

"Not something you see everyday. Better to be above it than below it,"  Key said.

As they flew over Key and Brownlee commented on the damage to rail lines and roads.

Key said he wanted Finance Minister Bill English and Transport Minister Simon Bridges to visit the area, as he and Civil Defence Minister Gerry Brownlee did today.

“It is a very, very big job for both the Transport Agency and Kiwi Rail,” said Key.

He thought it would be a very long time before State Highway One was operating in a major way.

The road was “utterly buried.”

“You’ve just to hope there is no car underneath that.”

Key said his message to the people of Kaikoura was to say New Zealand knew what they were going through.

“We are not blind to the size of the problems they are now encountering.”

The doors were opened and the helicopter flew low as the PM, Brownlee and Little surveyed the area.

The crew also ran through what other defence force personnel had been doing through the day. Some had gathered supplies to take in to Kaikoura. A number of NH90s are preparing to take in tonnes of food, water and other supplies tomorrow.

"It's really warm" Key said as he flew over the Clarence Rivermouth.

"It's a lot of water running down there."

Parts of the area were clearly impassable and the water was a murky brown.

The doors to the chopper were open as they flew over the hills and the dust was thick in the air.

"It's like a fire almost," Key said.

As he viewed the damage, Andrew Little said the mudslides and rockfall were "stunning".

"I can't imagine what it will be like to clear it," he told us.

As the plane descended sharply in to Kaikoura bumpy conditions large rockfalls were evident.

"Look at that road down there, it's been hammered," Key said.

A slumped hill could be seen and Brownlee commented "oh hell that's amazing".

They commented to each other and the pilots over the intercom about large slips on roads and the rail line.

Cars could be seen lying on their sides.

1200 tourists are stranded in Kaikoura. The Government is looking at options to try and help them get out.

They have surveyed the damage over Blenheim where Mr Key discussed with his Defence Minister the liquefaction that could be seen in some areas as the chopper flew low over the town. 

Traffic was flowing on State Highway One and only spots of damage could be seen. 

The flight then flew low over Seddon - an area of concern in previous quakes. 

Mr Key asked Mr Brownlee if Seddon had been badly hit. The pair are speaking to each other via an on-board intercom system. 

Mr Brownlee said not too many claims were lodged in the last quakes and the damage is not bad at all. 

Mr Little has praised the "amazing community spirit" in Kaikoura following this morning's severe earthquake.

Speaking to reporters in the South Island town, Little said the area was "pretty badly affected" with "a lot of houses damaged" after the 7.5 quake which struck just after midnight.

"They know they're isolated for a while but great community spirit, people supporting each other and pulling through. 

"This is a town that's based on tourism, that needs tourism traffic - it's now isolated. You've got hundreds of tourists here that are going to be wanting to get our in the next few days."

Little said supplies and provisions were arriving in Kaikoura.

"Anything the government can do to make sure that people can get in and out, supplies can get in and out, obviously we would support that. This isn't a time for politics, this is a time for supporting a community that's doing it real tough at the moment.

"Coming down you look at the damage to the roads, there's huge slips right across the roads, damage to rail. This is going to be a long time to get this fixed and a lot of money to do it."

Before leaving, Key said the failures of the 111 system last night were “deeply worrying.”

He was commenting on the emergency services response to the large earthquake last night during including the fact that the 111 system experienced delays in the worst hit areas.

What happened to the 111 system would need reviewing to see what took place.

“I don’t have an answer to what took place there but it obviously is deeply worrying.”

Brownlee ​told Larry Williams the phone line going down was "most unfortunate".

"In the end it was human error. Someone thought they had switched the system over when they hadn't, so that was out 30 minutes. That's pretty unacceptable but we have to figure out some was to ensure that never happens again."

Given the "magnitude of this event" and the distance over which the earthquake was felt, things "unfolded as well as could be expected".

"There's always something to learn but now we're focusing on the areas that have got the greatest recovery to go through."

Brownlee did not want to put a number on how much earthworks in damaged areas would cost, but said it was "not something that's going to be down easily or quickly, unfortunately".

"You don't like to give the dollars away too quickly but it's certainly going to cost a great deal of money."

There was "catastrophic damage" in the worst hit areas, including Kaikoura, which has been isolated by quake damage.

"We have had a brief meeting this afternoon with the Civil Defence people on the ground.

"We hope the inland road can be opened as quickly as possible so it's not cut off. It's going to be in a difficult situation for a while."

Despite this, Kaikoura residents were "in great spirits".

Key was less concerned about the tsunami.

The best advice from GNS was that because the quake had been on land it wasn’t going to cause a tsunami.

“The good news is we had very good systems and it was those indicators that measure the tide movement that alerted to us that the earthquake had moved the plates and moved out to sea.”

There would be a debrief afterwards.

“Initially I think you’ve got to say things have worked pretty well.”

Key said the office of Labour leader Andrew Little asked to join him on the tour which he readily agreed to.

Earlier today Key met Hungarian President Janos Ader who offered sympathy and support.