Millions of Muslim pilgrims began the annual hajj in Islam's holy city of Mecca, Saudi Arabia, Saturday. Saudi authorities are keeping a watchful eye to prevent tragedies like stampedes or tent fires from marring the event, as Edward Yeranian reports from Cairo.

A sea of white cloaked pilgrims crowd into the Grand's mosque in Mecca for the opening prayer of the five-day annual hajj pilgrimage.

Officials in Saudi Arabia say 2.5 million Muslim pilgrims are attending this year's hajj. Saudi government TV showed thick crowds of people, moving slowly throughout the city of Mecca.

Some were carrying flags to indicate their countries of origin, many elderly hajjis were using walking sticks to move around, and others could be seen carrying tin water flasks to quench their thirst.

Colder than usual temperatures had many hajjis, clad in the traditional ihram or two-sheet white cloak, shivering, and the normally ubiquitous umbrellas, to protect pilgrims from the often scorching sun were less visible than usual.

Pilgrims will spend Saturday night in tents outside of Mecca in an area known as Mina before beginning the ritual ascent of Mount Arafat on Sunday.

Hundreds of rows of tents were visible in aerial images shown on Saudi TV and Saudi officials are vowing to do their utmost to avoid any tragic tent-fires like those that have befallen the hajj in previous years.

General Mohammed Harby of the Saudi Civil Defense Corps explains that he and his men have deployed all their physical assets to prevent tragedies from occurring and to help the smooth flow of the hajj.

Harby says the civil defense forces are prepared for all possible scenarios during the hajj including floods, rescue operations, transporting injured people and putting out fires. He adds that logistical planning and coordinating the flights of hundreds of planes and helicopters is a major task that is handled by the civil defense operations center.

The climbing of Mount Arafat, outside Mecca, which gets under way Sunday is the high point of the annual pilgrimage, and the trajectory from inside the Prophet's mosque, to the summit of the mountain is meant to symbolize the epic journey of the Prophet Abraham, according to Professor Aweyd al-Matrafy of King Abd al-Aziz University.

Al-Matrafy says it is commonly thought that Ismail, Abraham's son, brought a stone to his father, the Prophet, who placed it where the Ka'aba, or holy stone, is located inside Mohammed's mosque. He argues that the stone may have grown to its present size and then the holy Ka'aba was built, at which point God ordered all men to perform the hajj. He adds that it is also possible that God stood over the stone and that it became the largest mountain in Mecca, or Mount Arafat.

Many Muslims believe their journey to Mecca and the pilgrimage will absolve them of their sins, and that they will return home with a fresh slate. The ultimate hajj ritual, the stoning of the devil on the final day of the pilgrimage, will give them the symbolic opportunity to cast aside evil.