The Grand Mosque and the cube-shaped Kaaba within it draw Muslims of all types from around the world throughout the year, though numbers increase significantly in the run-up to the annual Hajj pilgrimage, which takes place this month. Performing the pilgrimage once during one's lifetime is a duty for all able-bodied Muslims.
Several cranes surround the mosque to support an ongoing expansion and other construction work that has transformed the area around the sanctuary. Steep hills and low-rise traditional buildings that once surrounded the mosque have in recent years given way to shopping malls and luxury hotels - among them the world's third-tallest building.
Saudi Arabia's civil defense authority provided a series of rising casualty numbers on its official Twitter account. As of late Friday, it said those wounded in the disaster numbered 184.
Videos and photos posted by social media users showed a grisly scene, with police and onlookers attending to multiple bloodied bodies on the polished mosque floors.
Pan-satellite Al-Jazeera Television broadcast footage from inside the mosque compound said to be from the aftermath of the accident, showing the floor strewn with rubble and what appear to be pools of blood.
Another video, on a Twitter posting, captured the apparent moment of the crane's collapse during a heavy rainstorm, with a loud boom, screams and confusion.
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