More than 400 people were airlifted out of cut-off the South Island town yesterday, after a 7.5 magnitude earthquake near Hanmer Springs killed two people and caused widespread damage.
By 2am today, more than 1400 aftershocks had been recorded.
The HMNZS Canterbury is off the coast of Kaikoura, along with survey ship Wellington which has found the sea floor in South Bay has risen by half a metre.
The Navy plans to use two landing craft that can each take 50 people. Up to 200 could be on board by this afternoon.
Mr Key - who visited the area on Monday - has returned to the district and said entire mountains seemed to have moved in some places and it was hard to see how the road could be salvaged.
He made the observations about the damage wrought by Monday's massive earthquake to the Transport Minister Simon Bridges during their trip down on an RNZAF NH-90 helicopter.
It was Mr Bridges' first look at the slips and damage to the coastal State Highway One and the rail line.
Mr Bridges' verdict when he saw the first major slip was "pretty messy."
Speaking to each other over the helicopter radio system, Mr Key replied "that's not the biggest one by any stretch of the imagination".
Further down, Mr Key pointed out massive slips which had totally obliterated the road.
"Look at this road here, this is really stuffed and there's thousands of metres of it. I just don't see how you can ever repair that bit of road. The whole mountain has moved over."
He said on his earlier visit on Monday they had seen the northernmost damage.
"We thought 'that's not too bad.' Then we got to here."
As they went past the train marooned between two slips, Mr Key observed the train and driver had been saved by lucky timing.
"Being in the tunnel probably saved him."
Mr Key said one slip alone would have taken the road out for a while and cost a lot to fix.
NZTA spokesperson Mark Owen said one of the issues would involve bringing the slip down in a controlled manner, as well as having to work in a marine environment.
He was expecting satellite imagery today to allow them to assess exactly how many slips there were.
Mr Owen said there was also major bridge damage, "much worse than after the Christchurch earthquakes" on SH 70.
A ford would have to be put in place at one point to get the road open again.
In Kaikoura, a long line of helicopters waited, part of the effort to bring in supplies and take out stranded visitors.
Kaikoura MP Stuart Smith had arranged for local farmers and businesses to meet with Key.
He said water supplies were still a problem and there were concerns about diesel for farmers, as well as for companies such as Whale Watch because the lifting of the seabed in the earthquake had impacted on their ability to operate.