Officials said they expected around 1.5 million pilgrims to descend on the site, where they performed prayers and listened to the annual sermon from Saudi cleric Sheikh Abdulaziz al Sheikh.
Helicopters hovered overhead and thousands of troops stood guard to organise roads flooded by men, women and children streaming towards Mount Mercy.
The numbers are sharply down from last year, due to fears linked to the MERS virus and to expansion work.
Governor of Mecca province and head of the central haj committee, Prince Khaled al Faisal, said 1.38m pilgrims had arrived from outside the kingdom, while only 117,000 haj permits were issued for domestic pilgrims.
This puts the number of pilgrims this year at almost 1.5m, less than half of last year's 3.2m, after Riyadh slashed hajj quotas for foreign and domestic pilgrims because of massive construction works at the Grand Mosque in Mecca.
The pilgrims arriving yesterday were from nearby Mina where most of them spent the night following the traditions of Islam's Prophet Muhammad, who performed the rituals 14 centuries ago.
They had moved to Mina on Sunday from the holy city of Mecca, home to the Grand Mosque, Islam's holiest place of worship, which houses the cube-shaped Kaaba structure towards which all Muslims pray daily five times.
The haj, which officially ends on Friday, is one of the five pillars of Islam that every capable Muslim must perform at least once.