At least 345 Muslim pilgrims have died in a crush during the stone-throwing ritual at the Hajj pilgrimage in Saudi Arabia, officials say.
Hundreds of pilgrims have also been injured. A BBC correspondent at the scene in Mina saw dozens of bodies lined up on the ground.
The ritual has seen many lethal stampedes but the number of dead this time is the highest in 16 years.
After a crush in 2004, barriers and stewards were added to improve safety.
The stampede took place at the foot of the bridge of Jamarat, where pilgrims hurl stones at three pillars representing the spot where the devil is said to have appeared to Abraham.
An interior ministry spokesman, Maj Gen Mansour al-Turki, told the Associated Press news agency the crush happened after pieces of luggage spilled from moving buses in front of one of the entrances to the bridge, causing pilgrims to trip.
At least 289 people were injured, according to the Saudi Health Minister Hamad bin Abdullah al-Maneh.
With the local hospital in Mina overflowing, many victims of the crush were transported to medical facilities in Mecca and Riyadh, a doctor told AP.
Many of the victims were reportedly from south and south-east Asia.
More than two million people were thought to have been performing the rite at the time.
'Road of death'
Witness Abdullah Pulig, an Indian street-cleaner, described a scene of carnage.
"I saw people moving and suddenly I heard crying, shouting, wailing. I looked around and people were piling on each other. They started pulling dead people from the crowd," he told AP.
Suad Abu Hamada, an Egyptian pilgrim, told the agency he heard screaming and "saw people jumping over each other".
"It was like the road of death in there," said another pilgrim, quoted by Reuters news agency, who spoke of women fainting amid elbowing crowds.
Ambulances and police cars streamed into the area, as security forces tried to move people away from the scene of the accident.
The pilgrims were returning via Mina after performing the Tawaf al-Wada, a farewell ceremony that involves walking around the Kaaba - a cube-like building in the centre of Mecca's Great Mosque - seven times.
1987: 400 die as Saudi authorities confront pro-Iranian demonstration
1990: 1,426 pilgrims killed in tunnel leading to holy sites
1994: 270 killed in stampede
1997: 343 pilgrims die and 1,500 injured in fire
1998: At least 118 trampled to death
2001: 35 die in stampede
2003: 14 are crushed to death
2004: 251 trampled to death in stampede
The Tawaf al-Wada is performed after the Hajj has finished.
The stoning is the riskiest ritual of the Hajj, as worshippers jostle to try to target the stones, often causing weaker pilgrims to fall under foot.
In 2004, more than 200 pilgrims were trampled to death while performing the same ceremony.
The latest deadly stampede comes days after more than 70 people died when a hostel for pilgrims collapsed in the Saudi city of Mecca.
The Hajj is one of the five pillars of Islam and every able-bodied adult Muslim is obliged to perform it at least once in their lives.