Tens of thousands of worshippers clung to cars and buses as a sea of white-robed pilgrims made their way towards the valley of Mina, where they will spend the night in thousands of tents.
"
We are opposed to this war and with the will of God it won't happen
"
Abdel Latif bin Fadl, Tunisian pilgrim
This year's pilgrimage is taking place against the backdrop of a looming war with Iraq and growing anger among Muslims over the United States' policy towards the Arab world.
Saudi authorities have deployed thousands of troops to maintain order and have owed to use "an iron fist" against any "terrorist" group trying to disrupt the pilgrimage.
Police and armed guards lined the route to Mina, while armoured vehicles patrolled the roads and helicopters hovered overhead.
Prayers
The pilgrims began pouring out of Mecca, home to Islam's holiest shrine, early on Sunday morning, causing massive traffic jams.
They will stop off in Mina before trekking to Mount Arafat, about 20 kilometres (12 miles) south-west of Mecca, on Monday, for the culmination of the Hajj.
According to Islam, the prophet Muhammad delivered his last sermon on the mount, when the last passage of the holy Koran was revealed.
Although the trip to Mina is not a pilgrimage requirement, the trip to Mecca, traditional birthplace of Muhammad, is incumbent on all able-bodied Muslims at least once in their lifetime.
More than three quarters of the pilgrims have come from around the world, far exceeding last year's gathering, according to Saudi officials.
Threat of war
As the momentum towards war with Iraq gained pace, many pilgrims said they would pray for a conflict to be averted.
"We are opposed to this war and with the will of God it won't happen, " said Abdel Latif bin Fadl, a Tunisian pilgrim.
Others said they would pray for America's defeat.
"I hate America. It is the cause of Muslim and Arab disgrace," said Ahmad, an Egyptian pilgrim who had come from Qatar.
The Hajj ends on Tuesday, when the pilgrims will return to Mina and begin Eid al-Adha, the Feast of Sacrifice.