Saudi hajj authorities said on Wednesday, the final day for arrivals from abroad, that 1.5 million foreigners were expected by the end of the day to join 500,000 residents of the kingdom for the pilgrimage.
The authorities, who have taken measures to avoid the fire and stampede tragedies of previous years, are beefing up security measures in and around Mecca.
Police controlled the main entrances Wednesday to Islam's holiest city, allowing in only those people with hajj permits. Entry to the Mecca area was restricted to ease the movement of pilgrims.
Traffic police were posted on major roads and crossings, especially in the Grand Mosque area where the holy "Kaaba", a cube-shaped structure of marble and grey stone, is located. Around the world, Muslims pray in the direction of the Kaaba, which Muslims believe was raised by the prophet Abraham and his son Ismael.
Masses of the faithful -- men in two pieces of seamless white cloth and veiled women -- thronged the Grand Mosque in large numbers to circle the cube-shaped Kaaba seven times, which is the traditional greeting of worshipers to the holy shrine.
The faithful, while making the rotations around Kaaba, prayed passionately for God to forgive their sins, to accept their pilgrimage and to help Muslims prevail over their enemies.
Pilgrims then made the "saiy", a walk seven-times between two hillocks where Muslims believe Abraham's wife Hagar searched for water for her baby Ismael until she found the Zamzam spring.
The hajj -- which every able-bodied Muslim with the means must carry out at least once in a lifetime -- starts in earnest Saturday when the pilgrims move to Mina, a valley outside Mecca where they will be housed in fire-proof tents. The pilgrims will keep an all-night vigil in Mina, and on Sunday, the faithful will scale Mount Arafat, 12 kilometers (seven miles) away, to stand there until sunset.
Here, they will pray for forgiveness at the site of Prophet Mohammad's last sermon.
On Monday, the last day of the hajj and the start of the Al-Adha (sacrifice) feast, the faithful will sacrifice a sheep and they will also stone three pillars that symbolise Satan.
The stoning will continue for three successive days, with each pilgrim having to throw seven stones against the crudely-built pillars. According to tradition, Satan appeared three times to Abraham, Hagar and their son, Ismael, who each stoned the devil seven times to symbolise their contempt for him.
Saudi leaders last year hailed a trouble-free pilgrimage, without any major security incidents or epidemics.
Over the previous three years, Saudi Arabia spent 720 million dollars to cut down the risks of disaster during the hajj. Pilgrims' tents are now fireproof to prevent a recurrence of a blaze in Mina that cost 343 lives in 1997. But in 1998, at least 118 pilgrims died and more than 180 were injured in a stampede during the "Stoning of Satan" ritual.