MAKKAH (Agencies) - More than 2.5 million Muslims from all over the world on Saturday (today) will perform Haj in Saudi Arabia. Pilgrims on Friday began the rites of the annual haj, leaving Makkah for Mount Arafat, where the prophet Muhammad (PBUH) delivered his final haj sermon. Dressed in white, they flooded the streets as they headed towards Mina, around five kilometres east of the holy mosque. The day is known as Tarwiah (Watering) Day, as pilgrims traditionally watered their animals and stocked water for their trip to Mount Arafat, some 10 kilometres further on. Many pilgrims took buses, while others set off on foot for a village that comes to life for just five days a year. Others were using the Mashair Railway, also known as Makkah Metro, to go to Mount Arafat and its surrounding plains where they will gather for the peak Day of Arafat on Saturday. The Chinese-built railway will operate for the first time this year at its full capacity of 72,000 people per hour to ease congestions and prevent stampedes in which hundreds have been killed in past years. The dual-track light railway connects the three holy sites of Mina, Muzdalifah and Mount Arafat - areas that see massive congestion during the five-day pilgrimage. It will replace 30,000 cars previously used, said project director Fahd Abu-Tarbush. The train this year is restricted to the pilgrims coming from inside Saudi Arabia and Gulf states, as well as 200,000 pilgrims coming from south Asia, Tarbush told AFP. Mashair Railway will transport 500,000 pilgrims from Mina, passing by Muzdalifah, reaching to Arafat, in addition to one million pilgrims on the Tashreeq days, which are on the 11th, 12th and 13th of Zil Haj. Around 1.7 million Muslims descended on Makkah from around the world while between 700,000 and 800,000 pilgrims are coming from inside Saudi Arabia. The haj is one of the five pillars of Islam and must be performed at least once in a lifetime by all those who are able to make the journey, and it is a dream that can take years to come true. To me, this is a miracle. Ive been dreaming of going to haj for years, and this dream is now being fulfilled, 67-year-old Nigerian pilgrim Salahuldin Mohammed told AFP. Another pilgrim, 58-year-old Mohammed Sadoreen from the Palestinian territories, said: I couldnt believe the day has come when I would see this sacred place. This is the first time I come to haj. The haj will end on Sunday with Eidul Azha. Coping with the worlds largest annual human assembly poses a security headache for Saudi Arabia - guardian of the two holiest mosques in Makkah and Medina. Saudi authorities have numbered the buses and tents in Mina according to the countries from which the pilgrims have come to prevent chaos. The oil kingpin has invested billions of dollars over the years to avoid deadly stampedes. In January 2006, 364 pilgrims were killed in a stampede at the entrance to a bridge leading to the stoning site in Mina, outside Makkah, while 251 were trampled to death in 2004. In July 1990, 1,426 pilgrims were trampled to death or suffocated in a stampede in a tunnel, also in Mina. The deaths prompted authorities to dismantle the old bridge and replace it with a multi-level with one-way lanes to ensure a smooth flow of pilgrims. Saudi Arabia also launched a new $10.6-billion project for a new extension to Makkahs Grand Mosque to increase its capacity to two million worshippers. We havent faced any problems. I didnt expect all these services to be available, said 55-year-old pilgrim Abdulhadi Badran. Irans Shia pilgrims are another headache Saudi authorities are faced with during haj season. However, Crown Prince Nayef bin Abdul Aziz has dismissed any threat from pilgrims coming from Iran, despite rising tension between Tehran and Riyadh over an alleged Iranian plot to kill the Saudi envoy to Washington and past confrontations. The Iranians have always shown their respect for the haj, he said. A total of 97,000 Iranians - the maximum allowed for Iran under a Saudi system apportioning pilgrim quotas among the worlds biggest Muslim countries - are in the holy cities of Makkah and Medina, Iranian media said Monday. We hope this years haj (pilgrimage) will take place in a very calm and spiritual atmosphere, the representative of Irans supreme leader Ayatollah Ali Khamenei at the pilgrimage, Hojatoleslam Ali Ghazi Asgar, said last week. Saudi security forces have several times in the past confronted Iranian pilgrims holding anti-US and anti-Israeli protests. In 1987, Saudi police efforts to stifle such a demonstration sparked clashes in which 402 people died, including 275 Iranians. An Iranian official told AFP that Iranian pilgrims are this year going to hold their demonstrations within the boundaries of their own camps as they did in the past few years, to avoid confrontations with Saudi security forces.