A large construction crane toppled over and crashed into the Grand Mosque in the holy city of Mecca on Friday, killing at least 87 people and raising fears about the safety of the site before the yearly hajj pilgrimage that is expected to bring in millions of visitors to Saudi Arabiathis month.

Saudi Arabia’s civil defense authority reported the accident and the rising death toll on in its Twitter feed, saying that more than 180 people were injured.

Others posted videos said to show the crane falling amid heavy winds and rain as well as chaos inside the mosque facility as the machinery crashed through the building. Images circulated on social media of worshipers covered in blood resting on the mosque’s white marble floor and laborers removing green carpets and cleaning puddles of blood.

The Grand Mosque is the world’s largest and houses the Kaaba, the black cube that Muslims around the world pray toward and which they walk around during the pilgrimage.

The Saudi government is in the midst of a multibillion-dollar project to enlarge the mosque, and the site is currently ringed with cranes. Many other construction projects are also underway in Mecca, including for the world’s largest hotel, with 10,000 rooms, 70 restaurants and a helipad.

Saudi news media reported that the governor of Mecca Province, Prince Khaled Al-Faisal, had called for an investigation into the cause of the crane collapse.
The Al Jazeera television network said the crane had fallen in the midst of a severe rainstorm, suggesting weather may have played a role.

An Al Jazeera correspondent in Mecca, Hasan Patel, said witnesses had told him the crane smashed into the third floor of the Grand Mosque about 5:45 p.m. He said the mosque was packed with people in advance of the 6:30 p.m. prayer.

Up to three million pilgrims visit Mecca during the hajj.The Saudi authorities go to great lengths to keep pilgrims safe as they visit, but disasters have occurred.

In 2006, a stampede on a bridge that is part of the pilgrimage route left more than 300 people dead, and in 2004 a stampede there killed more than 200. The worst stampede, in 1990, claimed 1,400 lives.