A stampede killed at least 717 people and injured hundreds more at the Haj in Saudi Arabia on Thursday, in one of the worst-ever tragedies at the annual Muslim pilgrimage.
It was the second deadly accident to hit the pilgrims this month, after a crane collapse in Mecca killed more than 100.
The stampede broke out in Mina during the symbolic stoning of the devil ritual, the Saudi civil defence service said.
Internet video showed bodies in piles, surrounded by discarded personal belongings and flattened water bottles.
In some areas rescue workers laid bodies in long rows on stretchers, limbs protruding from beneath white sheets.
The civil defence said it was still counting the dead, who included pilgrims from different countries.
At least 863 people were hurt, the agency said.
Rescuers respond to a stampede that killed and injured pilgrims in the holy city of Mina during the annual hajj pilgrimage on Thursday. (AP)
Iran announced that 90 of its nationals were among the dead.
King Salman ordered "a revision of the plans" for haj organisation so that pilgrims can "carry out their rituals in complete safety", the official Saudi Press Agency said.
Nearly two million people from across the globe were attending the haj, one of the largest annual gatherings in the world.
A Saudi minister blamed the pilgrims for the tragedy, saying they had not followed haj rules.
"Many pilgrims move without respecting the timetables" set for the haj, Health Minister Khaled Al Falih told El Ekhbariya television.
"If the pilgrims had followed instructions, this type of accident could have been avoided."
Saudi Crown Prince Mohammed bin Nayef, who chairs the kingdom's haj committee, ordered an investigation, and King Salman said he wanted the results quickly, SPA reported.
'Tripping all over each other'
The stampede began at around 9:00 am (0600 GMT), shortly after the civil defence said on Twitter it was dealing with a "crowding" incident in Mina, about five kilometres (three miles) from Mecca.
Hundreds of thousands of pilgrims had converged on Mina to throw pebbles at one of three walls representing Satan, for the last major ritual of the haj which officially ends on Sunday.
Interior ministry spokesman General Mansur Al Turki said the stampede was caused when "a large number of pilgrims were in motion at the same time" at an intersection of two streets in Mina.
"The great heat and fatigue of the pilgrims contributed to the large number of victims," he said. Temperatures in Mina had reached 46 degrees Celsius (115 degrees Fahrenheit) Thursday.
The disaster came as the world's 1.5 billion Muslims marked Eid Al Adha, the Feast of Sacrifice, the most important holiday on the Islamic calendar.
Two million pilgrims
It was the second major accident this year for haj pilgrims, after a construction crane collapsed on September 11 at Mecca's Grand Mosque, Islam's holiest site, killing 109 people, including many foreigners.
The haj is among the five pillars of Islam, and every capable Muslim must perform it at least once in a lifetime.
For years it was marred by stampedes and fires, but it had been largely incident-free for nearly a decade following safety improvements.
In the last major incident, in January 2006, 364 pilgrims were killed in a stampede during the stoning ritual.
In 1990, 1,426 mainly Asian pilgrims died in a tunnel stampede at Mina after a ventilation system failure.
Thursday's tragedy occurred outside the five-storey Jamarat Bridge, which was erected in the last decade at a cost of more than $1 billion (893 million euros) and intended to improve safety.
Almost one kilometre (less than a mile) long, it resembles a parking garage and allows 300,000 pilgrims an hour to carry out the ritual.
Official figures released Thursday said 1,952,817 pilgrims had performed this year's haj, including almost 1.4 million foreigners.
There was little immediate information on the nationalities of the dead, though officials in Turkey said at least 18 of its citizens were reported missing.
Condolences came from capitals around the region and the globe, including from UN Secretary General Ban Ki-moon.
Washington calling the stampede "heartbreaking".
"We join you in mourning the tragic loss of these faithful pilgrims," said US National Security Council spokesman Ned Price.
British Prime Minister David Cameron tweeted: "My thoughts and prayers are with the families of those killed at the haj pilgrimage."
The faithful had gathered until dawn Thursday at nearby Muzdalifah where they chose their pebbles and stored them in empty water bottles.
Muslims worldwide commemorated Abraham's willingness to sacrifice his son by slaughtering cows, sheep and other animals on Thursday.
Celebrations of Eid Al Adha were also marred in neighbouring Yemen, where a suicide bomber struck a mosque in the capital Sanaa in an attack targeting Shiite worshippers.
At least 25 people died in the attack.