While safety experts said that it was too early to identify the exact case of the latest incident, it is likely to raise questions about the authorities' handling of the huge crowds of devout Muslims who visit Mecca every year. The pilgrimage - known as the hajj - is considered the duty of all observant Muslims.
The tragedy was the worst to befall the pilgrimage since July 1990, when 1,426 pilgrims were perished in an overcrowded pedestrian tunnel leading to holy sites near Mecca and the ninth in a string of such incidents since then.
Both stampedes occurred on Eid al-Adha (Feast of the Sacrifice), Islam's most important feast and the day of the stoning ritual. Over the last 25 years, such incidents have claimed the lives of more than 3,000 pilgrims.
Prince Mohammed bin Nayef, Saudi Arabia's crown prince who chairs the Saudi hajj committee, ordered an investigation during a meeting with senior officials responsible for the pilgrimage in Mina, where the stampede took place, Saudi Press Agency reported.
According to the Saudi civil defence directorate, the crowd became dangerously congested at the intersection of two streets, known as 204 and 223, as the faithful were making way towards the Jamarat Bridge, which overlooks the stone columns where pebbles are cast.
The bridge's purpose is specifically to ease the pressure of the crowds, which can reach three million during the busiest times of year.
Ambulance sirens blared as rescue crews rushed the injured to nearby hospitals, while more than 220 rescue vehicles and some 4,000 members of the emergency services were deployed to provide alternative exit routes.
Amateur video shared on social media showed corpses lying amid crushed wheelchairs used by some disabled pilgrims.
The tragedy comes despite the Saudi authorities installing sophisticated crowd analytics software which is linked to central control room where officials can analyse and predict where pinch-points and surges are likely to take place.
It was installed by a British company, CrowdVision, following the deaths of 346 pilgrims in 2006, but the firm told The Telegraph that their equipment did not cover the entire area.
"Our company has an active involvement in the Hajj, and the Saudi government has invested significant resources in this area," said Fiona Strens, CrowdVision’s co-founder. "But those resources have been invested mainly around the Jamarat Bridge area, where previous incidents have happened, rather than the scene where this latest incident took place."
Interactive: Mecca Stampede
She said she could not comment on why the technology had not been rolled out more extensively, and added that it was still too early to determine the exact cause of the accident.
The 2006 incident prompted a major safety overhaul, with the last nine years having been relatively trouble-free. Less than two weeks ago, a giant construction crane came crashing down on the Grand Mosque in Mecca, the focal point of the hajj. More than 100 people were killed.
Each year pilgrims pay hundreds of thousands of pounds to go on the religious trip, with people spending between £4,000-5,000 for a typical pilgrimage. More than 25,000 Britons go annually for the hajj, according to the British Hajj Delegation but there were as yet no reports of British casualties.
Among the pilgrims were individuals from Nigeria, Niger, Chad and Senegal.
Which countries have the largest number of hajj pilgrims?
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Foreign Secretary Philip Hammond said Foreign Office staff were checking hospitals to find out whether any Britons needed help and sending more staff to help with its response.
"I was saddened to hear of the enormous loss of life in Mecca. My thoughts are with families and victims at this difficult time. Such a significant tragedy will affect Muslims across the world who take part in the Hajj pilgrimage.
"Our staff remain in close contact with the Saudi authorities and tour operators, and are checking hospitals and other locations to urgently gather information about British nationals who may require assistance.
"We are also deploying further staff from the region to bolster our response."
Terrible scenes at #Mecca, my thoughts are with all those affected by this tragedy.— Philip Hammond (@PHammondMP) September 24, 2015
Professor Keith Still, an expert in crowd behaviour at Manchester Metropolitan University who was a special adviser on the Hajj from 2001 and 2005, said that Thursday's incident appeared to have taken place in area some distance from where previous tragedies had taken place.
He noted from satellite imagery, however, that it appeared to be at a spot where a wider road led to a narrower road. "Wherever that happens there is a potential risk but that is pure speculation at this stage," he said.
Prof Still, who has also lectured on crowd control issues at the British Cabinet Office's Emergency Planning College, added: "There is little we can say at this stage beyond it being an epic tragedy. When you have three million people in transit through a city like this, you are already dealing with an extremely congested environment, which poses a significant logistics issue."
He was, however, critical of Saudi Arabia's health minister, Khaled al-Falih, who appeared to blame the pilgrims themselves for the tragedy, saying they had ignored timetables for when to move through the city.
"If the pilgrims had followed instructions, this type of accident could have been avoided," Mr Falih told El-Ekhbariya television.
Prof Still said he was "speechless" at the minister's remarks. “Without knowing the facts, blaming the crowds is not appropriate," he said.
Crowd control experts generally prefer to avoid even using words such as "stampede", as that implies blame on the crowd itself rather than those responsible for managing them.
John Drury, an expert in crowd psychology at the University of Sussex, told The Telegraph: "In general, the reason why there are crowd crushes are because there are problems with management. People can't see how dense a crowd is when they are in one, they have what we call poor 'back to front communication'. So when it goes wrong you cannot blame the crowd because they are not in a position to be blamed."
Photographs published on the Twitter feed of the Saudi civil defence on Thursday showed pilgrims lying on stretchers while emergency workers in high-visibility jackets lifted them into an ambulance.
Safety during hajj is a politically sensitive issue for the kingdom's ruling Al Saud dynasty, which presents itself internationally as the guardian of orthodox Islam and custodian of its holiest places in Mecca and Medina.
Iranian leaders have been deeply critical of the Saudi authorities over what they charge were flawed crowd control measures. "The government of Saudi Arabia must accept the huge responsibility for this catastrophe," Iran's supreme leader Ayatollah Ali Khamenei said after 131 Iranian citizens died.
Said Ohadi, head of Iran's hajj organisation, accused Saudi Arabia of safety errors and said that for "unknown reasons" a path had been closed off near the scene of the symbolic stoning of the devil ritual where the accident later took place.
"This caused this tragic incident," he said on Iranian state television. In Turkey, Mehmet Görmez, head of Turkey’s religious affairs directorate, said 18 Turkish pilgrims were missing and believed to have been in the area where the tragedy took place.
Iran said it had also set up a special headquarters at the accident site to support Iranian pilgrims.
David Cameron was among many offering their condolences via Twitter. "My thoughts and prayers are with the families of those killed at the Hajj pilgrimage," the Prime Minister said.
The White House also gave its "deepest condolences" after the "tragic loss" as it said it joined pilgrims in their mourning.
"The United States expresses its deepest condolences to the families of the hundreds of Hajj pilgrims killed and hundreds more injured in the heartbreaking stampede in Mina, Kingdom of Saudi Arabia," said Ned Price, National Security Council spokesman.
"As Muslims around the world continue to celebrate Eid al-Adha, we join you in mourning the tragic loss of these faithful pilgrims."
Pope Francis also expressed solidarity with Muslims and voiced the "closeness of the church" in the face of the tragedy.
Source : http://www.telegraph.co.uk/news/worldnews/middleeast/saudiarabia/11887302/Eid-al-Adha-At-least-100-killed-and-hundreds-injured-in-crush-during-hajj-outside-Mecca.html