King Abdullah of Saudi Arabia will officially launch a $10.6-billion (7.3-billion-euro) extension project Friday for the Grand Mosque in Mecca, Islam's holiest city, media reports said.
The project is intended to allow the complex to accommodate some two million worshippers at a time, the daily Asharq al-Awsat said.
The site, where 10,000 workers are already working round-the-clock covers an area of 400,000 square metres (4.3 million square feet).
The project envisages a multi-level extension on the north side of the complex, together with stairways and tunnels to facilitate worshippers access to the mosque, built around the cubic Kaaba that all Muslims face to pray.
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The Grand Mosque underwent significant expansion in the mid-1980s, but the number of Muslim pilgrims has steadily grown, requiring another expansion.
Friday evening, Abdullah also is due to officially inaugurate the 601-metre (1,983-foot) Mecca Royal Clock Tower, topped with a gigantic four-faced clock that rises from behind the hills and helps visitors at other holy sites locate the Grand Mosque.
The clock tower is the world's second tallest building -- behind the Burj Khalifa, the 828-metre (2,717-foot) skyscraper inaugurated in Dubai early last year.
Mecca, which during the annual hajj pilgrimage attracts some 2.5 million Muslims from around the world for a stay of two weeks on average, last November opened a metro service that will operate only during the hajj season.
A proposed $10-billion (7-billion-euro) high-speed train linking Jeddah to Medina via Mecca is also in the cards, with European and Asian companies locked in fierce competition for the project.