Dust storm hampers quake recovery in Christchurch

Gusts of 70 kilometres per hour (44 mph) buffeted emergency crews in the ruins of New Zealand's second largest city, hampering the search for bodies amid fears of masonry dislodging and trees toppling.

"In some places it was difficult to stand up, you'd look across the city and see these enormous clouds of dust blowing down the main avenues – it's been a terrible day," mayor Bob Parker said.

The winds stirred an estimated 200,000 tonnes of silt and sand pushed up from the ground after the power of the 22 February quake loosened the bond between soil particles in a process called liquefaction.

Search and rescue teams donned respirators and dodged flying sheets of corrugated iron as they raked through the wreckage, while supplies of facemasks were rushed to Christchurch for residents.

The death toll from last week's 6.3-magnitude tremor stands at 160 today, climbing toward a final tally that police expect to exceed 240.

About 400 relatives of the dead visited the city's worst-hit sites in what Parker said was a difficult and emotional trip that he hoped would bring them some closure.

Rescuers have conceded they do not expect to find any more survivors, turning attention to questions about why the damage inflicted on the city in the 6.3-magnitude tremor was so severe.

Up to a third of the downtown area faces demolition and two office blocks concertina-ed in the violent 15-second shake and were completely destroyed.

City engineers deemed both office blocks safe after a major 7.0 tremor last September which miraculously resulted in no deaths in Christchurch, a result attributed at the time to New Zealand's stringent building standards.

Christchurch City Council building manager Steve McCarthy said the quake was a unique seismic catastrophe and it was lucky more office towers had not fallen.

He said last week's quake, though weaker in magnitude than September's, was shallower and closer to the city centre, hitting it with such force that it hurled buildings upwards, as well as side-to-side, before dropping them.