Violent aftershocks hampered desperate efforts to find survivors in quake-hit Christchurch on Saturday as the death toll climbed to 145 and New Zealand Prime Minister John Key called for a two-minute silence for the nation to grieve.

Rescue teams from New Zealand and six countries including the United States, China, Japan and Australia scoured ruined buildings in the central city and suburban areas hardest hit by Tuesday's 6.3 tremor -- but found only bodies.

"We expect that number to rise as the search and rescue teams progressively find more and more deceased among the ruins," police commander Dave Cliff told reporters.

The dead include people from 20 nations, including Israeli Ofer Mizrachi, as well as dozens of students from Japan, China, India and Taiwan who were in Christchurch, one of New Zealand's most attractive cities, to learn English in view of the country's dramatic southern Alps.

Hopes of finding people alive five days after the quake were dimmed by aftershocks of up to magnitude 4.4 which brought down masonry and sent rescue teams scrambling for safety.

Key called for a two-minute national silence on March 1 as a sign of unity for the people of Christchurch, New Zealand's second largest city, and to grieve for people killed in the country's worst natural disaster for 80 years.

"For now we must do all we can to show its people that all of New Zealand grieves with them," said Key, who met with the families of those still missing.

"They fear the worst but there is still a glimmer of hope," he said. "The urban search and rescue crew made it clear that this was still very much a rescue effort, not a recovery.

No survivors have been rescued since mid-afternoon on Wednesday. The number of missing remains at more than 200, but police have said it is likely that the number includes recovered bodies that have yet to be identified.

Rebuilding

Earthquake Recovery Minister Gerry Brownlee said rebuilding plans were already underway for the ruined centre, but much of the financial district could be sealed off for months as a "huge demolition effort" of up to a quarter of the buildings began.

Early estimates of insurance losses have ranged from $3 billion to over $ 12 billion.

"When we do rebuild the type of building will have to pass an economic test for future use and it will have to meet pretty stringent (building) code requirements," Brownlee said.

"That doesn't deter us from doing that, the prospects for this city are quite bright there are not many other cities that get to completely rebuild."
In the central city, the search concentrated on a finance company office block, the city's landmark cathedral and a local television building, which housed an English language school, but aftershocks hampered efforts.

"Work did have to stop there temporarily during the period of falling masonry," said Cliff.

More than half of the dead have come from the ruins of the Canterbury Television (CTV) building. About 61 people, including 26 Japanese and 13 Chinese students, attended the school where floors pancaked down on one another.

More than 600 rescue workers scoured the city and hardest-hit suburbs, where broken water and sewage pipes, toppled power lines and ruptured gas mains have made large areas uninhabitable, forcing thousands to flee.

In the devastated eastern suburbs nearest the quake epicentre, where hundreds of homes have been marked with red tape for demolition, Andre de Roo pumped water for neighbours from a backyard well near a makeshift sign reading "must boil".

"It's almost my duty to share it with everybody," said de Roo.

Authorities are concerned about an outbreak of gastric disease in the city, prompting frustration that repair efforts are not continuing fast enough.

Bob Parker, the local mayor, appealed for patience as services were slowly restored in the city of 400,000, New Zealand's second biggest.

"This will not get easy in a hurry," Parker said. "The next few days as we try to work as hard as possible on restoring services, we need to ask that you support us. Nobody is sitting back watching this. Everybody is involved."

Thousands of volunteers from unaffected parts of the city or nearby towns converged on the worst-affected areas, shovelling away sun-baked mud and sand contaminated with sewage and debris.

Ratings agency Standard i Poor's backed New Zealand's ability to withstand the massive economic impact of the quake, saying the country's AA+ foreign rating was secure, albeit with an existing negative outlook.