Images posted by social media users showed a grisly scene, with police and onlookers attending to numerous bodies lying amid pools of blood on the polished mosque floors.
Saudi Arabia's civil defense authority provided a series of rising casualty numbers on its official Twitter account as ambulances whisked the wounded to area hospitals. As of early Saturday, it said those injured in the disaster numbered 238.
A photo released by the authority showed police and workers in hardhats inspecting a pile of collapsed concrete slabs inside a part of the sprawling, ornately decorated mosque. Another showed the base of the toppled red-and-white crane tilted upward at a sharp angle.
Ahmed bin Mohammed al-Mansouri, the spokesman for the presidency of the Mecca and Medina mosque affairs, said in a statement carried by the official Saudi Press Agency that the accident happened late Friday afternoon during a severe storm carrying strong winds and heavy rain.
The governor of the Mecca region, Prince Khalid al-Faisal, quickly called for the formation of a committee to investigate the cause of the accident. He directed all appropriate authorities to provide support for all of those injured, according to a statement from Mecca principality public affairs head Sultan al-Dosari that was carried on SPA.
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, a giant clock tower that is the centerpiece of the Abraj al-Bait complex.
The construction giant Saudi Binladin Group is leading the mosque expansion and also built the Abraj al-Bait project.
The Binladin family has been close to the ruling Al Saud family for decades and oversees major building projects around the country. The Binladin family disowned one of its many members, late al Qaeda leader Osama bin Laden, in the 1990s.
It was not immediately clear who owned the crane that collapsed.
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 hajj. The mosque is Islam's holiest site to which Muslims face in daily prayers and a central site among the hajj rituals.
Performing the pilgrimage once during one's lifetime is a duty for all able-bodied adult Muslims. This year's pilgrimage is expected to start around Sept. 22