Wednesday's devil-stoning marks the start of the three-day Eid al-Adha holiday, celebrated by Muslims by buying and slaughtering livestock to commemorate Abraham's willingness to sacrifice his son.
Mina's walkways have proven deadly in the past: in 2015, a stampede killed up to 2,300 worshippers in the worst hajj disaster ever. A similar incident killed 364 in 2006.
Other stampedes were reported in 2004, 1998 and 1994. In 1990, the failure of a tunnel ventilation system triggered a huge rush that killed 1,426 pilgrims, mainly from Asia.
There have been no major incidents since 2015, and the site has been extensively remodelled with a multi-storey bridge to allow the pilgrims to access the monoliths safely.
The scorching conditions have been perhaps the biggest challenge for this year's worshippers, including many elderly after a maximum age limit was scrapped.
In recent years the hajj, which follows the lunar calendar, has fallen in the Saudi summer, at a time when global warming is making the desert climate even hotter.
Experts have warned that temperatures of 50 degrees Celsius could become an annual occurrence in Saudi Arabia by the end of the century.
As protection from the heat, many pilgrims have been walking with umbrellas to shield themselves from the sun, while others carry their folded prayer blankets above their heads.
One security guard was seen fanning a seated pilgrim, apparently overcome by the heat at Mina. According to official figures, at least 287 people have been treated for heat exhaustion and heatstroke.
On his way out of Arafat on Tuesday, Sobhi Saeed, a 56-year-old Egyptian, said he was fulfilled but drained as the hajj winds down.
"I am very exhausted. I feel very dehydrated."
The rituals started on Sunday at Mecca's Grand Mosque, Islam's holiest site, before an overnight stay in tents and then the prayers on Mount Arafat, where the Prophet Mohammed is believed to have delivered his final sermon.
