At least 863 others were injured at Mina, a few kilometers east of Mecca, when two large groups of pilgrims arrived together at a crossroads on their way to performing the "stoning of the devil" ritual at Jamarat, Saudi civil defense said.
Thursday's disaster was the worst to occur at the pilgrimage since July 1990, when 1,426 pilgrims suffocated in a tunnel near Mecca. Both incidents occurred on Eid al-Adha (Feast of the Sacrifice), Islam's most important feast and the day of the stoning ritual.
Photographs published on the Twitter feed of Saudi civil defense on Thursday showed pilgrims lying on stretchers while emergency workers in high-visibility jackets lifted them into an ambulance.
Other images showed bodies of men in white haj garments piled on top of each other. Some corpses bore visible injuries.
Unverified video posted on Twitter showed pilgrims and rescue workers trying to revive some victims.
The haj, the world's largest annual gathering of people, has been the scene of numerous deadly stampedes, fires and riots in the past, but their frequency has been greatly reduced in recent years as the government spent billions of dollars upgrading and expanding haj infrastructure and crowd control technology.
Safety during haj 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.
Saudi Arabia's Crown Prince and Interior Minister Prince Mohammed bin Nayef bin Abdelaziz ordered a committee to be formed to investigate the disaster and present its findings to King Salman, the Interior Ministry said.
The ministry spokesman, Mansour Turki said the investigation would look into what caused an unusual density of pilgrims to congregate at the location of the disaster. "The reason for that is not known yet," he told a news conference in Mina.
Iranian state news agency IRNA said at least 89 Iranians were among the dead and quoted Iran's Deputy Foreign Minister Hossein Amir Abdollahian as saying Saudi Arabia was responsible.
The semi-official Fars news agency reported that Tehran summoned the Saudi charge d'affaires to lodge an official complaint over the disaster.
South African Acting President Cyril Ramaphosa extended condolences to families of the victims and said his government was awaiting information about his country's pilgrims.