Nearly 2 million Muslims on Sunday packed Mount Arafat near the holy city of Mecca in Saudi Arabia marking the peak of the annual Hajj pilgrimage.
Saudi authorities have tightened security across the holy sites for the five-day Hajj that started on Saturday to prevent the recurrence of a stampede that caused hundreds of deaths last year.
This year's event has been free of trouble so far, said a spokesman for the Interior Ministry, Mansur al-Turki.
Clad in seamless pieces of white cloth, the pilgrims, gathering in Arafat, prayed for God's forgiveness and contentment.
They canted in unison: "Here I am at your service, O God. Here I am, at your service. You have no partner."
The pilgrims' snow-white garments symbolize equality, religious unity and pursuit of spiritual renewal.
This year's Hajj is being held amid a war of words between Saudi Arabia and its regional rival Iran over the handling of the pilgrimage.
Addressing the faithful on Arafat, a prominent Saudi Muslim cleric praised Saudi leaders for what he called their "double efforts in serving pilgrims."
"Security of the two holy mosques as well as safety of pilgrims are red lines that cannot be crossed," Abdel-Rahman al-Sudais, the imam of the Grand Mosque in Mecca, said in his sermon.
The second holiest mosque is that of the Prophet Mohammed in the Saudi city of Medina.
Earlier this week, a Saudi government minister said that Iran does not want the pilgrimage to pass safely.
Iranians are absent from this year's Hajj due to a row with the Saudis on pilgrimage regulations.
The pilgrims, now in Saudi Arabia, will stay on Arafat until sunset Sunday when they will head to the nearby plain area of Muzdalifah to stay overnight.
In Muzdalifah, they will also collect pebbles to use for a symbolic stoning of the Devil ritual on Monday in the desert valley of Mina, around 7 kilometres north-east of Mecca.
Some 769 Muslim pilgrims died in a stampede during the stone-throwing ritual in last year's Hajj, according to Saudi official figures.
A dpa tally and other independent reports, however, indicated that around 2,000 pilgrims died in the crush.
About 1.8 million Muslims are attending this year's Hajj, according to Saudi officials.
Authorities have stepped up security to tightly control the crowd.
The measures include the installation of hundreds of surveillance cameras in the holy sites.
Saudi officials have said that camera-bearing drones, linked to control centres, are also being used to monitor the pilgrims' movements at the holy sites.
Digital bracelets have also been issued to the pilgrims to help identify and guide them in the congestion. The bracelets are connected to a GPS location system.
Devout Muslims are expected to perform the Hajj, one of Islam's five pillars, at least once in their lifetime, provided they are fit enough and have the financial means to do so.