The slips over the roads were huge - equivalent to four the size of the Manawatu Gorge slip.
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."
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."
Viewing the region from the air revealed extensive damage to essential connections and basic infrastructure, Acting Civil Defence Minister Gerry Brownlee said.
"The Prime Minister and I have now seen first-hand the numerous major slips, which have isolated Kaikoura from the north and south, he said.
"The widespread destruction caused by the magnitude 7.5 earthquake and subsequent aftershocks will take considerable time and resources to repair.
"The roads and railways are things that can be repaired in time but it's important to think of those who lost their lives today or suffered injuries."
One person was killed was Kaikoura homestead collapsed in the quake, while another person in Mt Lyford suffered a heart attack and died.
"Our immediate priority is ensuring delivery of clean water, food and other essentials to the residents of Kaikoura and the estimated 1000 tourists in the town," Brownlee said.
"The New Zealand Defence Force has been tasked with delivering the essential items Civil Defence is asking for - first by NH90 helicopters, which have already made a number of runs, and also on board the Canterbury.
"Other areas affected by today's earthquakes and consequential landslides, including Hanmer, Waiau and Marlborough, have adequate communication and supplies at this stage."
The economic impact on earthquake-affected areas will also be assessed in the coming days.
"Any suggestions the Earthquake Commission will be financially stretched in meetings its obligations are ill-founded. EQC is guaranteed by the Crown," Brownlee said.
"This has been a trying day for communities across many parts of the country, particularly those on the east coast of the South Island and Wellington region."
Agencies will continue monitoring the situation closely and aftershocks are expected to continue.
"It's important that people look out for each other," Brownlee said.
Brownlee said the deployment of HMNZS Canterbury would support the ongoing response.
The transport ship had been due to take part in the international naval review to mark the Navy's 75th birthday but has been deployed to help evacuate people trapped in Kaikoura.
Brownlee, who is also Minister of EQC, said any suggestion that the Earthquake Commission would be financially stretched in meeting its obligations were ill-founded.
"EQC is guaranteed by the Crown."
The latest annual report says it has access to $4.69 billion of reinsurance protection.
As at June 30 June 2016 EQC had paid out $9.4 billion in response to the 2010 - 2011 Canterbury earthquakes.
Its aim was to have cashed settled the more than 14,000 claims for those earthquakes by the end of the year, then chief executive Ian Simpson said.
He said that while EQC had assets of $2.1 billion and liabilities of $2.5 billion at the end of the financial year, EQC had adequate funds to continue to operate and to meet its financial obligations because the Crown had confirmed it would meeting its obligations under law to ensure the EQC met its liabilities as fell due.
