"It just started with a group of people pushing their way in and then finally they just got trapped and people started to step on bodies under their feet," one pilgrim told CBS Radio News.
The tragedy underlined the difficulty in managing one of the biggest religious events in the world, which this year drew more than 2.5 million pilgrims. It is the second deadly incident of this hajj pilgrimage, followingthat killed 76 people Jan. 5 in Mecca.
In the stoning ritual, all the pilgrims must pass by a series of three pillars called al-Jamarat, which represent the devil and which the faithful pelt with stones to purge themselves of sin.
The site in a desert plain of Mina outside Mecca is a notorious bottleneck in the week-long hajj pilgrimage and has seen deadly incidents in seven of the past 17 years, including a stampede in 1990 that killed 1,426 people and another in February 2004 that killed 244.
"I heard screaming and ... saw people jumping over each other," said Suad Abu Hamada, an Egyptian pilgrim, who was nearby when Thursday's stampede broke out.
"Police starting pulling out bodies. The bodies were piled up. I couldn't count them, they were too many," she said.
Afterward, bodies were lined up on the pavement nearby, covered with white sheets, and emergency workers rushed the injured away on stretchers. Police cleared part of the site, but thousands of pilgrims continued the stoning ritual nearby.
The Interior Minstry said 345 people were killed. State-run Saudi television Al-Ekhbariyah reported that most of the victims were from South Asia. The Health Ministry said 289 people were injured.
Since the 2004 stampede, Saudi authorities widened ramps leading to the platform where the three pillars are located and created more emergency exits to accommodate the crowds.
The small, round pillars were replaced with 26-meter-long walls to allow more people to stone them at once without jostling each other. The walls extend down through the bridge and protrude underneath, so pilgrims below can also carry out the stoning without going above.
Thursday's stampede occurred below the platform, near one of the entrance ramps.
"While the Saudi government tried very hard to provide the infrastructure, it's just simply an issue of overcrowding," Mehdi Hassan, a reporter with Sky News, told CBS News. "There are just too many people."
Thousands of pilgrims were rushing to complete the last of the three days of the stoning ritual before sunset, when some of them began to trip over dropped baggage, causing a large pileup, Interior Ministry spokesman Maj. Gen. Mansour al-Turki said.
Many pilgrims carry their personal belongings — such as tents, clothes or bags of food — with them as they move between the various stages of the hajj.
Mina General Hospital, a small facility several hundred yards from the site, was filled with injured, and some victims were sent to hospitals in Mecca and Riyadh, said Ismail Abdul-Zaher, a doctor at the hospital.
Many pilgrims expressed frustration over the repeated disasters at al-Jamarat.
"This should not happen every year. It should be stopped, it's a scandal. There must be a way to organize this better." Anwar Sadiqi, a Pakistani pilgrim, said.
Ensuring a smooth pilgrimage is a key concern for Saudi Arabia's royal family, which bolsters its legitmacy by touting its role as the "custodian of the holy cities" — Mecca and Medina, where Islam's 7th century prophet Muhammad was born and lived.
The annual hajj is a complex balance of safety with Islam's requirements that every able-bodied Muslim should perform the hajj at least once. Saudi Arabia sets a quota of participants, allowing every nation to send 1,000 pilgrims for every 1 million in population.
The stoning ritual in particular is a nightmarish problem in crowd dynamics.
Hundreds of thousands of pilgrims must move up the ramps onto the platform — which is several hundred yards long and the width of an eight-lane highway in parts — maneuver from pillar to pillar and hit each with seven stones, then exit the platform.
Many of the pilgrims are in a rush because of time constraints on the ritual and are nervous because they remember the past stampedes.
Traditionally, the stoning is carried out from midday to sunset. Shiite Muslim clerics have issued fatwas, or religious edicts, allowing pilgrims to do the stoning in the morning, and some Sunni clerics have followed suit in an attempt to space out the crowds.
But some clerics following Saudi Arabia's strict Wahhabi interpretation of Islam advise the faithful to stick to the midday start.
About 60,000 Saudi troops have been patrolling the Mina plain since the stoning ritual began on Tuesday to direct pilgrims. Helicopters fly overhead, and authorities monitor the pilgrims from a control room through closed-circuit television.
But some complained the police did little to help the flow of traffic.
"They look indifferent. They don't carry out their duties seriously," Iftikhar Hussein, an Iraqi pilgrim, said. "This looks like a garage rather than a holy site."
"If hajj is a duty for every able-bodied Muslim, it should be a duty for the government" to ensure it is safe, she said.
Signs giving directions are few, and pilgrims often ignore regulations, entering the platform via ramps meant for exiting and vice versa. Peddlers selling food and souvenirs also mingle among the pilgrims, jamming up traffic.
Saudi Arabia has announced plans for further changes to the site in coming years that it says would allow some 500,000 pilgrims an hour to carry out the stoning.
Among the changes, the platform is to be expanded to four levels, with 12 entrances and 12 exits. Also, there are plans to bus pilgrims to al-Jamarat from a nearby tent city in the desert rather than allowing them to make their own way to the site.
Thursday evening, the highway from Mina to Mecca was packed with buses, trucks and cars carrying pilgrims back to the holy city for the final rite of the hajj — the "farewell tawwaf," or circumambulation of the Kaaba, the black stone cube that all Muslims face when they perform daily prayers. The hajj ends on Friday.