More than 2.5 million Muslims will on Friday begin the annual hajj pilgrimage in the Islamic holy city of Mecca, Saudi Arabia, against a backdrop of tensions in the Gulf.
Crowds of worshippers have already begun to gather in Mecca in the days ahead of the hajj, the focal point of the Islamic calendar.
"It's the first time I've felt something so strongly -- it's striking," said 40-year-old Indonesian pilgrim Sobar in rudimentary Arabic.
More than 1.8 million visitors had arrived by midday local time on Tuesday, authorities said.
Crowds of faithful from across the world wore flowing white robes as they descended on the holy city located in the west of the ultra-conservative kingdom.
The pilgrims will undertake religious rites that have remained unchanged since the founding of Islam 14 centuries ago.
"Islam united us. We are all together... so that's why I'm very happy," said Leku Abibu, 46, a Ugandan mechanic who wore a beige salwar kameez. "I'm enjoying it here."