In the ruins of his two-storey home, 11-year-old Mohammed gathers chunks of the fallen roof into a broken pail and pounds them into gravel which his father will use to make gravestones for victims of the Gaza war.

“We get the rubble not to build houses, no, but for tombstones and graves - from one misery to another,” his father, former construction worker Jihad Shamali, 42, says as he cuts through metal salvaged from their home in the southern city of Khan Younis, destroyed during an Israeli raid in April.

The United Nations estimates there is over 42 million tonnes of debris, including both shattered edifices that are still standing and flattened buildings.

That is 14 times the amount of rubble accumulated in Gaza between 2008 and the war’s start a year ago, and over five times the amount left by the 2016-17 Battle of Mosul in Iraq, the U.N. said.

Piled up, it would fill the Great Pyramid of Giza - Egypt’s largest - 11 times. And it is growing daily.