Strong winds whipped up huge dust clouds in earthquake-hit Christchurch on Wednesday, as officials defended the devastated city’s building standards.

Gusts of 70 kilometres per hour 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.

“The conditions have been difficult, the wind is picking up and it’s very dusty in the inner city, which is making the rescue efforts more difficult,” district police commander Dave Cliff told reporters.

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

Search and rescue teams donned respirators as they raked through the wreckage, while supplies of facemasks — stockpiled around the country in case of an influenza pandemic — were rushed to Christchurch for residents.

The death toll from last week’s 6.3-magnitude tremor stood at 159 on Wednesday, climbing toward a final tally that police expect to exceed 240.

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 city centre’s buildings face demolition after the quake left them cracked and teetering, while two office blocks concertinaed and were completely destroyed.