Nearly 2 million Muslims packed Mount Arafat Thursday, near the holy city of Mecca in Saudi Arabia, marking the peak of the annual hajj pilgrimage.
Helicopters flew around the area as the faithful converged from dawn on the surrounding Mount Arafat plain and the hill known as Jabal al-Rahma -- or Mount of Mercy.
Dressed in white, the pilgrims could be seen climbing up the sides of the hill and taking up positions to pray on rocks already heated by the morning sun.
Most of them were sitting or walking carrying green and yellow umbrellas, to avoid the scorching sun.
The pilgrims will stay on Mount Arafat from dawn until dusk, spending the day praying and reciting the Quran.
The pilgrims' snow-white garments symbolize equality, religious unity and the pursuit of spiritual renewal.
It is believed that Mount Arafat is where Prophet Mohammed delivered his final sermon around 14 centuries ago.
There was tight security across the holy sites for the pilgrimage that started Wednesday, with 100,000 security personnel deployed.
The pilgrims will head to the nearby area of Muzdalifah in the plains, where they will also collect pebbles to use for a symbolic stoning of the Devil ritual in the desert valley of Mina, around 7 kilometers north-east of Mecca.
Mecca is Islam's most sacred site, where Muslims go each year to perform the hajj.
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.
The ritual at the Jamarat Bridge was the scene of a stampede in 2015 that claimed the lives of 2,300 pilgrims -- the worst disaster in the history of the hajj.
At the foot of Mount Arafat, mobile barriers have been installed to control the movement of the crowds.
"They will be moved to enlarge the passages when there are more pilgrims," said Ahmed al-Baraka of the Saudi security forces.
The kingdom has deployed more than 100,000 security personnel to keep pilgrims safe at this year's hajj, according to the interior ministry.