The 111 emergency line service wasn't switched over when the Spark office where the calls are handled was evacuated.
The 111 emergency line outage after this morning's earthquake was caused by human error.
Speaking to Newstalk ZB, Acting Civil Defence Minister Gerry Brownlee said 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."
Spark's Wellington office answers and redirects emergency calls and was damaged and evacuated immediately after the earthquake. The service would usually be switched to another call centre in an emergency.
The telco said in a statement that the team making the switchover procedure during the quake were impeded by falling ceiling tiles and air conditioning equipment, which landed on the very desk being used to make the switch.
"While staff believed they had completed the procedure, it became apparent after they had urgently left the building that the procedure had not worked properly," Spark said.
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".
