Saudi Arabia's usually deserted Mina valley burst with life as more than three million Muslim pilgrims stoned pillars representing Satan on Friday, first day of the Eid al-Adha holiday.
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.
Men, women and children linked only by faith advanced in waves around Jamrat al-Aqaba, the largest of three adjacent pillars, in the rite that lasts until Sunday.
The ritual marks the start of one of the most sacred Muslim holidays.
"Allahu akbar (God is greatest)," a hunched and bearded old man shouted every time he threw one of seven stones at the pillar.
Beside him, tears streamed down the face of a couple who raised their hands to the heavens in prayer. Their child proudly hurled a stone at the pillar, echoing the old man's cry.
"My feelings are a mixture of happiness and sadness," said Abdullah Noor, a 47-year-old Malaysian after he finished stoning. "I'm happy because I managed to reach this holy land -- a dream I have had for years.
"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 the biblical patriarch from obeying God's order to sacrifice his son, Ishmael.
Roads inside Mina and leading there were choked with pilgrims.
They had stopped to collect their stones overnight in Muzdalifah, another holy town that comes to life only during the hajj, before heading to Mina.
Several kilometres (miles) from the pillars, male pilgrims sat on the ground, shaving each others' heads and filling the place with hair.
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.
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Red Crescent and civil defence helicopters overflew 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.
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.
Official figures put the number of registered pilgrims this year at 3.16 million. But hundreds of thousands more perform the pilgrimage without permits.
Among the facilities used to ease the movement of humanity between the holy sites is the Mashair Railway linking Arafat, Muzdalifah and Mina.
But chaos was reported at railway stations as pilgrims fought to board trains, despite tickets being pre-booked. No injuries were reported, but Mecca governor Prince Khaled al-Faisal ordered an investigation.
Interior Ministry spokesman Mansur al-Turki told reporters on Friday that the congestion was caused by pilgrims without permits.
Faisal said that 50 percent of the pilgrims have made use of the train which had to delay its operations for 90 minutes on Thursday after the station was flooded by 150,000 illegal pilgrims.
The train with a capacity of no more than 530,000 pilgrims ended up transporting 680,000 people on Thursday.
Meanwhile in Mecca, where pilgrims must perform the "Tawaf" circumambulation around the Kaaba -- the cube-shaped stone structure towards which Muslims worldwide face for prayer -- one pilgrim was killed in a bus collision.
The Saudi Red Crescent announced that one person was killed and 15 others suffered light to medium wounds when two buses carrying pilgrims collided Friday in the holy city of Mecca, state news agency SPA reported
After the first stoning, sacrifices are offered with the slaughter of a sheep whose meat is distributed to needy Muslims.
The rite emulates Abraham who prepared to sacrifice his son before God provided a lamb in the boy's place at the last moment.