|Hopes of finding survivors continue to fade as the death toll from the Christchurch earthquake increases [AFP]
New Zealand 's prime minister has warned the country may be facing its greatest tragedy as the death toll from the earthquake in the city of Christchurch surges to 145, with another 200 missing.
John Key said on Saturday that last week's tremor, which toppled office buildings and rained debris on Christchurch streets, "may be New Zealand's single most tragic event", outstripping a 1931 quake which killed 256 people.
Officials say entire blocks will have to be razed after the disaster, which left up to a third of the city centre facing demolition along with parts of outlying suburbs, and cut power and water supplies to most of the 390,000 population.
Key, who met relatives of those dead and missing in the stricken city, announced a tribute of two minutes' silence on March 1, one a week after the quake struck at 12:51 pm on Tuesday.
He said the silence was a chance "to stop and remember those who have lost their lives, those who are missing, and the hundreds of people who are mourning family and friends".
Key also said relatives were fearing the worst, three days after rescuers now numbering in their hundreds last detected any signs of life in the twisted wreckage.
"I think it's fair to say they [relatives] fear the worst but there is still a glimmer of hope," he said.
"They are full of fear because a significant period of time has elapsed."
Police said 145 bodies had been taken to a temporary morgue, and that there were "grave concerns" for the 200 listed as missing. They include a large number of Asian students feared lost in a collapsed language school.
Al Jazeera's Andrew Thomas, reporting from Christchurch, said that bodies that may be found will be difficult to identify.
Engineers said on Saturday that as much as a third of the central district, where office buildings folded like packs of cards and entire streets lost their shop frontages, may have to be demolished and rebuilt.
"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]," Jason Ingham, a structural engineer from Auckland University, told local media.
Power has now been restored to most of the city but many of its 390,000 residents are without water and relying on supplies brought by tanker.
Officials said more than 62,000 homes have no water supplies and 100,000 properties are without sewerage, while 800 portable toilets were being put in place to help ward off the threat of disease.
Al Jazeera and agencies