Vast crowds of Muslim pilgrims flocked to Mount Arafat on Thursday to perform the main hajj rites, with those from Arab Spring states praying fervently for freedom and stability.

Men, women, and children from 189 countries streamed from dawn to the site in western Saudi Arabia, some setting up small colourful tents in which they slept and prayed.

Beggars and street vendors also dotted the roads searching for generous souls among the 2.5 million believers expected to converge on the plain for the most important rituals of the five-day hajj.

According to Mecca governor Prince Khaled al-Faisal, around 1.7 million people had travelled from abroad for the pilgrimage, many of them from Middle Eastern countries which have been shaken by Arab Spring uprisings.

On the vast plain surrounding Mount Arafat, prayers reflected the instability sweeping the region.

"God destroy Bashar," prayed 30-year-old Mohammed Ahmed, referring to Syrian President Bashar al-Assad, as he stood atop the "Mount of Mercy" in Arafat plain.

His mother nudged him nervously, urging him to keep quiet. "Now regime troops will kill our whole family back home" in Syria's northern Idlib province, swathes of which -- but not all -- are under rebel control.

In the crowds, Syrian worshippers were seen carrying a large rebel flag, a symbol of the 19-months-long deadly uprising against Assad's regime in which according to activists more than 34,000 people have died.

The Syrian government did not send any pilgrims this year, but hajj visas were granted to Syrian refugees in Jordan and Lebanon.

Libyan pilgrim Ruqaya al-Fayturi, 58, told AFP she was praying for "security and stability in Libya and all other Arab and Muslim countries."

The region was hit by a wave of uprisings that began in 2010 toppling autocrats in Tunisia, Egypt, Libya and Yemen. In Syria meanwhile, the once peaceful mass protests against Assad have degenerated into a bloody civil war.

For Mai, a 34-year-old Egyptian, the hajj is a "gift" from God that she will use to pray for "victory and peace in Egypt and all Muslim countries," she said.

Others who descended on the plain from early morning focused on the religious significance of the day.

"We came from Mecca. We walked from the Grand Mosque to Mina and then we took the buses to Arafat. All for the love of the prophet," said one Egyptian man sitting on a straw mat with members of his family.

"The more tired we get, the more God will reward us," he said.

Focus of the rituals is the "Mount of Mercy" where the Muslim Prophet Mohammed is believed to have delivered his final hajj sermon before his death.

Many pilgrims made themselves comfortable between the huge rocks, tears streaming down their faces as they prayed.

A preacher urged pilgrims not to climb the slippery stone staircase leading up the hill, bellowing over loudspeakers: "Neither the prophet, nor his followers have ever climbed the hill. Please do not climb it."

Pilgrims have in previous years slipped and fallen while attempting the ascent, and others have been killed in stampedes.

After sunset, the pilgrims head to Muzdalifah, between Mina and Arafat, where they collect stones to throw at the devil, one of the last rituals which takes place Friday and marks the first day of Eid al-Adha, the feast of sacrifice.

The symbolic "stoning of the devil" is followed by the ritual sacrifice of an animal, usually a lamb.

During the remaining three days of the hajj, the pilgrims continue the stoning ritual before performing the circumambulation of the Kaaba shrine in Mecca and heading home.

The hajj is one of the five pillars of Islam that every capable Muslim must perform at least once.

More than 100,000 members of the security and civil defence forces have been deployed to ensure the safety of the pilgrims, while some 3,000 CCTV cameras have been installed across hajj sites.