The governor of the Makkah region, the capital of which is Mecca, Khalid al-Faisal has ordered the launch of an investigation into the causes of the accident.
The tragedy comes ahead of the annual Hajj pilgrimage which is due later this month. Millions of Muslims from around the world will converge on the holy city between September 21-26.
Photos taken from the scene and posted on social media show bodies lying in blood on the mosque’s floor surrounded by construction rubble and metal parts of the crane.
Over 68 emergency and rescue groups are active at the scene of the accident, the Saudi Red Crescent said on Facebook.
Director General of the Civil Defense Authority, confirmed to al-Ikhbariya television that storm winds had uprooted trees and affected cranes in the area.
"All those who were wounded and the dead have been taken to hospital. There are no casualties left at the location,” he added.
The project to expand the mosque was launched in 2011 by late King Abdullah bin Abdulaziz. Earlier in 2015, King Salman bin Abdulaziz added five construction projects as part of the mosque’s expansion aiming to accommodate more than 1.6 million worshippers.
The projects cover 1.47 million square meters and include the construction of 78 new gates at ground level, according to the official Saudi Press Agency. The project and is being carried out by the Saudi Binladin Group at an estimated cost of US$26.6 billion, according to local press.
The Grand Mosque, or Sacred Mosque, surrounds the Kaaba – the most sacred site in Islam. The cuboid structure made of granite located in the mosque’s center is often called the House of Allah.
The Kaaba is the place of the Hajj – the Islamic pilgrimage to Mecca, which is one of the five Pillars of Islam. It is mandatory of all Muslims physically and financially capable to carry out the journey at least once in a lifetime. The period of Hajj in Mecca is considered to be one of the largest gatherings of people in the world.