Police have delayed releasing the names of those confirmed dead and for whom there are serious concerns.

Initially the details were going to be released from 4pm but now police say Canterbury District Commander Superintendent Dave Cliff willprovide an update on progress with the lists at a media briefing at 6pm this evening at the Christchurch Art Gallery.

Superintendent Dave Cliff said earlier at a Christchurch media conference that the names of confirmed dead and the 238 listed as missing would be released.

Prime Minister John Key had earlier told media in Wellington that the names of the missing would be made public but his staff then informed reporters that the Prime Minister had been incorrect and only the numbers of missing would be detailed.

At his media conference, Mr Key said only the dead who had been positively identified and whose families had been informed would be named.

He it would only be a small number today, and some families were not comfortable yet with their loved ones names being released.

Mr Key said there were international protocols that police had to go through before the details of foreign nationals could be released.

But he said he was satisfied police were going through the correct processes in identifying victims and that it was important the information was accurate.

Early indications were that there could have been fatalities from a number of countries, he said.

Mr Key also gave an indication of the scale of destruction wreaked by the 6.3 magnitude quake on Tuesday - saying thousands of homes are likely to be rendered uninhabitable.

Forty teams of four people are to be sent into the city's suburbs today to assess damage, he says.

He expected them to find far more damage than after the 7.1 magnitude earthquake on September 4 which left 3000 homes uninhabitable.

Mr Key was to take a call from President Barack Obama before flying to Christchurch early this afternoon where he and Finance Minister Bill English would be speaking with business leaders.

As previously indicated, given the damage the central city, the economic fallout from this week's quake was expected to be far greater than the one in September.

The economic support package required would need to be broader and of a slightly different nature to last time. Mr Key hope to make some initial announcement on a package early next week.

Mr Key also said Earthquake Recovery Minister Gerry Brownlee was to give up his other portfolios to concentrate on the quake recovery.

Simon Power would take over as Leader of the House, David Carter would become acting Minister for Economic Development, and Hekia Parata was to become acting Minister of Energy and Resources.

The missing

Mr Key earlier said he believed a "sizeable" number of people were missing.

He revealed some of his own friends might be among the missing and said he could appreciate the frustration felt by those who still did not know the fate of their families and friends.

"I myself have got one or two people I think might be missing and I personally would like to know the status of them."

There have been issues putting a number on how many people are actually missing as many people may have left town following the quake without telling anyone, he said.

"The longer someone has been missing and expected home, the more likely they have been caught up in the disaster - but it doesn't mean they are dead," Mr Key said.

"The problem with missing numbers is we don't know the starting point of how many people were still in a building and how many left. Obviously we know when a loved one rings up and says 'my husband/ wife/ child has not come home' we can track that down more easily. It's when you get into the international potential fatalities it becomes a much more complex picture," Mr Key said.

He said on the best advice available, it appeared there were fatalities from several countries and he expected to know further by the end of the day or tomorrow.

While he appreciated the frustration of not knowing, he believed the police were doing the best they could.

"In the end the niceties sometimes go out the window and the number one focus is to get people out. That's where police have been focussed with the search and rescue teams and in the end I think that's the right call. If we can save someone, we have to try to save them."

He said if someone was still missing it did not mean there was dead as there was a very 'real' possibility people were still trapped alive but unable to communicate.

Police were sending dogs in "but they're not getting a huge number of positive responses from the buildings that we would expect there to be more people trapped alive."

Next of kin had been contacted in some cases, he confirmed.

"The priority must be with families, but there are also friends."

- NZ Herald staff