Rescuers digging through the rubble after Morocco's deadly earthquake warned on Monday that the traditional mud brick, stone and rough wood housing ubiquitous in the High Atlas mountains reduced the chances of finding survivors.

"It's difficult to pull people out alive because most of the walls and ceilings turned to earthen rubble when they fell, burying whoever was inside without leaving air spaces," a military rescue worker, asking not to be named, said at an army center south of the historic city of Marrakesh not far from the quake epicentre.

Morocco's most powerful earthquake since at least 1900 has killed at least 2,497 people, the state news agency said in its latest update of the human toll on Monday, with thousands more injured and many still missing.

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With many homes fashioned out of mud bricks and timber or cement and breeze blocks, in an area not accustomed to powerful earthquakes, structures crumbled easily in mounds of debris when the quake struck late on Friday, without creating the pockets of air that earthquake-ready concrete buildings can provide.

"That is a very brittle material ... and in an earthquake it doesn't have sufficient deformability to absorb the shock. It cracks very quickly, and then it crumbles very quickly," said Colin Taylor, of the University of Bristol.

"You've basically got a pile of rocks and mud dust and that just congeals together ... you're being buried underground by all this material ... packing itself around you," said Taylor, an Emeritus Professor of Earthquake Engineering.

These homes, sometimes hundreds of years old, sometimes built more recently, can be found across the mountains, and have long been a popular sight for tourists traveling from Marrakesh.

Homes are often built by the families themselves in a traditional pattern, without any architect's help and with extensions added when they can. With no major earthquakes for a long time, few people would have thought to consider the risk of a tremor.

This meant even concrete homes or buildings often lack anti-seismic design, experts said, leaving survivors and rescuers to sift through mounds of rubble where homes once stood.

"The big government decision is really around making sure you use modern construction forms in any rebuilding. Rebuilding in this mud brick form is just going to create the next disaster in 20 or 30 years time," Taylor said.

Many survivors across the area have spent three nights outside, their homes destroyed or rendered unsafe. In Adassil, south of Marrakech, people moved to a tented camp after their houses were destroyed by the earthquake, the hamlets flattened and transformed into mounds of rubble.

With much of the quake zone in remote areas, the full impact has yet to emerge.

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