Saudi Arabia has opened investigation after at least 107 pilgrims were killed when a giant construction crane collapsed on the roof of the Grand Mosque in Mecca.
The crane, one of 15 placed around the holiest site in Islam, appears to have been toppled by high winds.
During a sudden storm, the crane snapped in half and smashed through the ceiling on the eastern side of the largest mosque in the world.
The Masjid al-Haram, or Grand Mosque, was particularly busy at the time, as Muslims converge on the site ahead of the annual Hajj pilgrimage at the end of the month.
Pictures and videos posted on social media showed scores of dead bodies on the mosque's marble floor and courtyard, with dazed and bloodied pilgrims being treated among the rubble.
Abdel Aziz Naqoor, who said he works at the mosque, said he saw the crane fall after being hit by the storm.
"If it wasn't for the Al-Tawaf bridge the injuries and deaths would have been worse," he said, referring to a covered walkway that surrounds the holy Kaaba and broke the crane's fall.
Prince Khaled al-Faisal, the governor of Mecca, has ordered an investigation into the incident.
This will presumably focus on why the crane was not properly secured against high winds.
However, the results of official inquiries are rarely disclosed in Saudi Arabia, which is instinctively secretive.
The €17 billion expansion of the Grand Mosque was being carried out by the Saudi Binladin Group, the industrial conglomerate founded by the father of Osama bin Laden.
A huge hotel complex is being built around a mile south of the Grand Mosque. The hotel, with 45 storeys and 10,000 bedrooms – including five floors for the sole use of the Saudi royal family – will be the largest in the world when it opens next year.
The Grand Mosque is Islam's most sacred site.
At its heart is the Kaaba – a black cube-shaped building – which Muslims all over the world face when they pray. Hajj pilgrims perform a series of rituals, including walking anti-clockwise seven times around the Kaaba.
The pilgrimage, one of the largest religious gatherings in the world, this year takes place between September 21-26.
Last year more than two million people performed Hajj, while in 2012 the figure was more than three million.
The official Saudi SPA news agency said in a statement that by yesterday, almost 800,000 pilgrims had already arrived in the kingdom.
The pilgrimage has suffered numerous disasters in the past, including fires and stampedes.
The worst stampede, in 1990, left 1,400 people dead.
The Saudi authorities have since gone to great lengths – and spent billions of euro – to expand the main Hajj sites and improve Mecca's transportation system.