More than three million pilgrims have gathered in the Mina neighbourhood of Mecca to celebrate the first day of the Eid al-Adha holiday.
Saudi Arabia's usually deserted Mina valley burst into life on Friday as more than three million Muslim pilgrims stoned
pillars, meant to represent the devil, marking the start of one of the most sacred Muslim holidays.
Worshippers from 189 countries swarmed the streets to the sound of prayers and sermons through loudspeakers, with security forces on full alert.
White tents dotted the valley surrounded by rocky hills, as fluorescent lights flooded the usually empty town into which the world's largest annual gathering, the Hajj, breathes life for five days each year.
Muslims marked the holiday, commemorating Prophet Abraham's willingness to sacrifice his son Ismail - as a test of his faith from God.
Around the world, Muslims slaughtered lambs, sheep and other livestock in remembrance, giving the meat to the poor.
In Mina, pilgrims purchased tokens to have a sheep slaughtered at nearby slaughterhouses.
'Atone for sins'
The day of stoning marked an exhausting trek for pilgrims between the string of ritual sites strung across the desert outside Mecca.
They spent the day on Thursday at Mount Arafat in a day of contemplation and prayers to wipe away past sins
Men, women and children advanced in waves around Jamrat al-Aqaba, the largest of three adjacent pillars, in the rite that lasts until Sunday.
"Allahu akbar (God is greatest)," a hunched and bearded old man shouted every time he threw one of seven stones at the pillar.
"But I'm sad because I couldn't bring my family with me." Daud Baev, a 65-year-old Kazakh, said: "This is the time to atone for the sins committed over the years."
The ritual is an emulation of Abraham's stoning of the devil at the three spots where he is said to tried to dissuade him from obeying God's order to sacrifice his son, Ishmael.
Meanwhile, the Saudi Red Crescent announced that one person was killed and 15 others suffered light to medium wounds when two buses carrying pilgrims collided in Mecca, state news agency SPA reported on Friday.
Official figures put the number of registered pilgrims this year at 3.16 million.
But hundreds of thousands more perform the pilgrimage without permits, which the Saudi interior ministry has cited as a reason for the traffic congestion and chaos at railway stations.
According to the authorities, 168,000 police officers and civil defence personnel were mobilised for this year's Hajj, and for the stoning, they organised specific times of day for groups of pilgrims to perform the ritual.
After the stoning ritual, male pilgrims shave or cut their hair while women trim the length of a finger-tip from one strand of hair.
The pilgrims then change back into normal clothing from white shrouds that symbolise the resurrection.
Red Crescent and civil defence helicopters flew over the area all day as a precaution.
Mina used to be the most dangerous phase of the hajj for the Saudi authorities, as it has been marred by deadly stampedes in the past as well as by fires in tent camps.
In recent years, however, tents have been fire-proofed and gas canisters and cooking are now banned.
The stoning area has also been expanded to avoid overcrowding. Saudi authorities have built a five-level structure around the three stoning sites, allowing for a smooth flow of pilgrims.
King Abdullah, who performed the vows in Mina, discussed instability in the region with officials and urged security officers to "act against those who would dare harm the security, unity and sovereignty" of the kingdom.