Tuesday's quake killed at least 145 people; some 200 are still missing.
Prime Minister John Key said there was still a glimmer of hope survivors could be found in the wreckage of the country's worst-ever disaster.
But no-one has been found alive since Wednesday, and rescuers working for a fifth day are only finding bodies.
In the meantime, engineers say at least a third of the buildings in the centre of Christchurch will need to be demolished, while hundreds of damaged suburban homes may also have to be pulled down.
Mr Key said the disaster "may be New Zealand's single most tragic event", outstripping a 1931 quake in Napier which killed 256.
He said a two-minute silence would be held on Tuesday at 1251 local time (2351 GMT Monday), a week after the quake struck.
Having met relatives of the dead and missing, Mr Key said: "It's fair to say they fear the worst but there is still a glimmer of hope."
Families of the missing have appealed for the process of identifying dead bodies to be accelerated, but officials have asked for patience.
Updating the lists of the dead and missing was a slow and methodical process, said police spokesman Dave Cliff.
"We are going through it as fast as we possibly can in order to get the deceased reunited with their loved ones," he said.
Rescuers from 10 countries, including Britain, Japan and the United States, have been searching broken buildings and piles of debris, as aftershocks continue.
Emergency worker Phil Parker said teams of eight to 12 people were still going into buildings, but said the work was tough and unpredictable.
"We won't be going into buildings that are deemed unsafe, that's why we're checking them now, but there's always that danger of the buildings coming down on us," he told the BBC.
Many damaged buildings will have to be pulled down, said Auckland University structural engineer Jason Ingham.
"We've collected some data over the past couple of days and it's looking like about one-third of the buildings (would be condemned)," he told TVNZ.
For many residents, it is all too much, and there is an exodus from Christchurch, says the BBC's Phil Mercer in the city.
Officials believe up to 22 bodies may lie beneath the rubble of Christchurch Cathedral; as many as 120 are thought to have been killed inside the collapsed CTV office block, including Japanese, Chinese and Philippine nationals; many others are presumed dead inside the destroyed Pyne Gould Guinness building.
Power has been restored to most of the city but water supply remains a problem, with residents being urged to boil water for drinking or cooking due to contamination fears.
The quake struck at a shallow depth of 5km (3.1 miles) early on Tuesday lunchtime, when the South Island city was at its busiest.