Nearly three million pilgrims chanting prayers converged Saturday in a valley just outside the holy city of Mecca at the beginning of the five-day hajj pilgrimage, a lifelong dream for many Muslims.

Muslim pilgrims pray during Friday prayers inside the Grand Mosque in Mecca, Saudi Arabia. (Hassan Ammar/Associated Press)

The pilgrims from about 100 countries left Mecca after completing the first ritual of the hajj by circling seven times the sacred Kaaba stone structure inside the Grand Mosque, which Muslims all over the world face during their five daily prayers.

Dressed in white robes, pilgrims piled into and on top of buses on their way to a ritual of prayer and reflection in Mina, five kilometres east of Mecca.

The journey caused massive traffic jams on roads to Mina, where pilgrims will spend the night in white, fireproof tents. Some pilgrims chose to walk the route.

The hajj, packed with symbolism and ritual, is one of the five pillars of Islam. Every able-bodied Muslim who can financially afford to make the pilgrimage must perform it at least once in his or her lifetime.

For Ahmed Malek, a pilgrim from the Maldives, the hajj teaches all people are equal before God.

"Here, all the people are wearing identical white dress, no matter who they are," said Malek.

"I get the lesson that all human beings will be judged on the basis of their deeds — not colour, race or social position."

Mohammad Hossein Salem, an Iranian pilgrim performing the hajj for the first time with his wife, said he waited 10 years to make the journey.

"Now, my dream has come true," said Salem. "Here is the best place to be on Earth."

Saudi Arabia has deployed about 100,000 security personnel to keep order during the hajj. Thousands of them patrolled the route to Mina on foot and in vehicles.

The high point of the pilgrimage comes Sunday with prayers at Mount Arafat, a gentle hill about 20 kilometres east of Mecca where the Prophet Mohammed is said to have given his last sermon 14 centuries ago. Muslims believe the last passage of their holy book, the Qur'an, was revealed to Mohammed during this sermon.

At Arafat, pilgrims offer prayers from noon to shortly after nightfall in a ritual that's interpreted as a foretaste of the Day of Judgment, when Islam says every person will stand before God and answer for his deeds.

Following the prayers, the pilgrims travel to nearby Muzdalifah to pray and collect rocks to throw at a pillar symbolizing the devil in Mina on Monday. After the symbolic stoning, the pilgrims slaughter a camel, sheep or cow to mark the beginning of the Eid al-Adha, or the "Feast of the Sacrifice."

The feast commemorates God's gift of a ram to substitute for Abraham's impending sacrifice of his son and is considered the most important holiday in the Islamic calendar.

The pilgrims remain in Mina for two more days to perform a second and third symbolic stoning of the devil and then perform a farewell circling of the Kaaba before leaving Mecca.