Prime Minister John Key flew into Christchurch to what he says were scenes from a horror movie.

"It's utter devastation," Mr Key told the Herald.

"Where we were blessed that the September earthquake took place when there were very few people around, this is the polar opposite: a busy Christchurch, people at work, people out shopping, children at school, so it's happened at the worst possible time, and on the back of weakened infrastructure from the 4000-odd aftershocks since the initial shock in September.

"That was a situation where people's lives were badly affected and where their possessions were destroyed, but those things can be replaced. You can't replace people who have lost their lives.

"And last time there was damage to the CBD, it was nowhere near as widespread as it is now. Frankly it looks like a scene out of a horror movie."

Mr Key was quick to hear from his sister and was relieved to learn she, her sons and husband were all right.

"But they're very badly shaken and their house is extremely badly damaged, not liveable. Last time they had a big shake, but no significant damage. It's a different story this time.

"Christchurch people are very resilient people and they will regroup, but the challenge is there are likely to be a significant number of aftershocks, and they are very unnerved.

"You can see the sheer fear and anxiety they are facing as they come to terms with what's happened to their city and what might happen in the next few months. That fear is palpable.

"It's hard to put into words. It feels much worse than last time because you know there is potentially a very significant loss of life."

The initial focus was on urban search and rescue teams freeing people trapped in a number of critically damaged buildings, including Canterbury TV, Smiths City, the Cathedral and Pyne Gould Guinness.

"It's hard to know how many people are potentially alive, how many have got out and how many have perished. That's something we're trying to get information on," Mr Key said.

An Australian search and rescue team was flying out overnight, and a second team was expected today.

The United States had also offered assistance.

"The second major focus is major infrastructure. We have significant issues with water, power, sewage and telephones. Once we've taken care of that and the immediate issue of housing people overnight, then there is the much broader issue of where we go from here."

The cost of the September earthquake was $7 billion, Mr Key said.

"Where last time the plan was to regroup very quickly and get back to business, we will have to check every building in the CBD again to satisfy ourselves that those buildings are safe. The CBD could potentially be out of action for a very long time.

"The total bill, I don't know. The first one was $7 billion and there is a lot more damage this time."

A compensation package for those unable to work would soon be worked out, he said. "While we had those in place last time, the sense is it will be greater this time."