The world's largest annual pilgrimage, the hajj, began with more than two million Muslims pouring into the camp at Mina from Mecca to prepare for the solemn rituals.
Some estimates put the number of pilgrims this year at 2.5 million, posing a major headache for the Saudi authorities as many of them are not hajj permit holders.
Pilgrims were still flooding on Sunday night into the vast plain of Mina outside a small village about five kilometres (three miles) east of Mecca, using all possible means to begin their hajj journey.
Permits were granted to 1.7 million foreign pilgrims, but the head of the Hajj Supreme Committee, Interior Minister Prince Nayef bin Abdul Aziz, on Sunday put the number of foreign pilgrims at a record 1.8 million.
A further 200,000 permits were issued to pilgrims from within Saudi Arabia and from neighbouring Gulf states.
|Muslim pilgrims walk on top of Noor mountain where the Hiraa cave is located overlooking Mecca|
An interior ministry official said definite numbers will not be announced until Tuesday, the first day of Eid Al-Adha or the Feast of the Sacrifice.
A driver caught transporting unauthorised pilgrims faces a fine of 10,000 riyals (2,667 dollars) for each one.
But the "No permit, no hajj" rule appeared to be widely flouted on Sunday as unauthorised pilgrims converged on Mina from across Saudi Arabia.
"We came from Riyadh," said a Palestinian after being dropped off with two companions at a junction leading to Mina and Arafat, as others arrived in pick-ups, taxis and small buses.
"We skirted the checkpoints by getting out of the car and walking across," he said without revealing his name, pointing out that once past the highway's main police checkpoints, getting to the sites is easy.
Buses, choked with both people and luggage inside, carried yet more on their roofs. Tens of thousands of illegal pilgrims sat on the pavements, many with tents.
"We don't have permits," said Ramadan Ismael, an Egyptian in his mid-50s who also came from Riyadh. He said a policeman let his group of 14 through even though they told him: "We have no permits."
Meanwhile, pilgrims in licensed groups sat comfortably in their enclosed and well-equipped camps.
The passage to Mina marks the official launch of the hajj on the eighth day of the Muslim calendar month of Dhul Hijja.
The day is known as Tarwiah (Watering) as pilgrims in the past stopped at Mina to water their animals and stock up for the trip to Mount Arafat.
At Mount Arafat, some 10 kilometres (six miles) southeast of Mina, the day is spent in prayer and reflection.
Some pilgrims by Sunday evening had already camped on the plain of Arafat, instead of at Mina, shortening the upcoming trip to the hill.
After sunset, they move to Muzdalifah, half way between Mount Arafat and Mina, to spend the night.
On Tuesday, they return to Mina after dawn prayers for the first stage of the symbolic "stoning of the devil" and to make the ritual sacrifice of an animal, usually a lamb.
On the remaining three days of the hajj, the pilgrims continue the ritual stoning before performing the circumambulation of the Kaaba shrine in Mecca and then heading home.
This year has been incident-free since the pilgrims began gathering in Mecca. The city's Grand Mosque has been flooded with the faithful, with an estimated 1.7 million taking part in the main weekly Muslim prayers on Friday.
The movement of pilgrims between the holy sites is a major worry for the authorities who have had to deal with deadly stampedes in the past.
Saudi Arabia has used its huge oil revenues for massive spending on new infrastructure to ease the flow of humanity.
This year, the first phase of the new Mashair Railway -- or Mecca metro -- will transport pilgrims between Mina and Mount Arafat through Muzdalifah.
The Jamarat Bridge, where the ritual of stoning takes place, has also been expanded to five levels with movement channelled in one direction.
Security is also a concern.
On Wednesday, the interior minister said he could not rule out the possibility of an Al-Qaeda attack, but on Sunday Al-Qaeda in the Arabian Peninsula (AQAP) said it is against targeting the hajj.
"We assure our Islamic nation that we are against any criminal action aimed at the pilgrims," it said in an online statement.