Two million Muslims began arriving in Arafat on Friday, (December 29) at the start of a haj pilgrimage with Saudi authorities on alert to prevent deadly overcrowding as well as sectarian violence. Moving in cars, vans and on foot, a mass of white-robed pilgrims poured into Arafat to begin the gruelling five-day ritual, a duty for every able-bodied Muslim who can afford to make the trip. In one of the world's biggest displays of mass religious devotion, pilgrims converge on the Grand Mosque in Mecca and follow a route around the mountains of the ancient city in line with a tradition established by the Prophet Mohammad. "I feel great happiness especially here in Arafat. It is considered one of the core events of the haj. It is the most important part of haj. I feel great here with the presence of all these people. We ask God to accept our pilgrimage," said Ali Kashem. "It is a great feeling to come here. I cannot express myself. Thank you." said an unidentified pilgrim. Asked if he came from very far away., he added: "Very far. From Bangladesh." With such large crowds, Saudi Arabia normally deploys more than 50,000 security men to try to avoid deadly stampedes and attacks by Islamists fighting the U.S.-allied Saudi royals. The authorities say they will crack down hard on Muslims who try to sneak into Mecca without official permits -- a phenomenon that can swell numbers by 500,000 to more than 2.5 million. State media said a record 1.65 million pilgrims had come from abroad, a 6 percent rise on the last haj. In January, 362 pilgrims were crushed to death due to overcrowding at the Jamarat Bridge during the last haj season. The toll was the worst on the bridge for 16 years and followed the death of 76 people in a hotel collapse in Mecca. Saudi Interior Minister Prince Nayef has said improvements introduced this year would prevent overcrowding at the bridge, which for three days from Saturday will witness the symbolic stoning of the devil, the most incident-prone haj ritual. Saturday, Sunday and Monday -- the last three days of the haj -- will be the key test of the new arrangements. Saudi Arabia has allocated $1.1 billion to expand the Jamarat Bridge into a multi-storey structure. The first phase, completed in time for this week's haj, allows up to 250,000 pilgrims to move across the bridge each hour. The haj takes place in the shadow of violence between Sunnis and Shi'ites that has taken Iraq to the brink of civil war. Sunni-Shi'ite tension is also high in Lebanon, where Shi'ites are leading efforts to bring down a Sunni-led cabinet. Iranian and other pilgrims have used the haj for political protests in the past. Shi'ite Iran is at loggerheads with the West over its nuclear plans and its backing of Shi'ite groups in Arab countries, raising the potential for trouble at the haj.