MINA: Some two million Muslims thronged Mina Valley from the holy city of Mecca to start the annual hajj pilgrimage Sunday, with numbers down on fears of the MERS virus and Saudi cuts.

Authorities announced at noon that all the pilgrims had reached Mina from nearby Mecca, following in the footsteps of Prophet Mohammed (PBUH) some 14 centuries ago.

Saudi Interior Minister Prince Mohammed bin Nayef said the number of pilgrims from outside the country totalled 1,379,531 million, down 21 per cent on last year's 1.75 million.

Around 1.29 million of them had flown to Saudi Arabia from 188 countries, he said, without giving a figure for pilgrims residing in the kingdom whose number is believed to have been halved.

The kingdom cut by 20 per cent the quotas for pilgrims allowed in from abroad over fears of MERS and because of massive projects to expand the capacity of the Grand Mosque, Islam's holiest place of worship.

Saudi Health Minister Abdullah al-Rabia told reporters late Saturday the authorities had so far detected no cases among the pilgrims of the MERS virus which has killed 60 people worldwide, 51 of them in Saudi Arabia.

Authorities have stepped up measures to curb illegal pilgrims who infiltrate into Mecca through desert roads.

Security officials have said that as many as 31,000 Saudi and expatriate pilgrims were turned back for not carrying legal permits, while around 12,600 others were arrested.

The pilgrims moved to Mina by road, by train or on foot, the men wearing ihram, the seamless two-piece white garment that rituals require, the women covered up except for their faces and hands.

In Mina, a small site with 45,000 fire-resistant tents that can accommodate two million people, they will pray and rest before moving on to Mount Arafat on Monday for the climax of the pilgrimage rituals.

A newly-constructed electric railway transported around 400,000 of the pilgrims taking part in the world's largest annual gathering.

Saudi Arabia has deployed more than 100,000 troops to ensure the safety of the pilgrims and has warned it will tolerate no demonstrations or disturbances.

Security forces are monitoring the holy sites in and around Mecca with 4,200 hi-tech cameras, some of which can cover a distance of 60 kilometres (37 miles).

Authorities said more than 20,000 buses are ferrying the pilgrims to Mina, using 58 tunnels under Mecca's mountains.

But some pilgrims, like Egyptian Mustafa Abu el-Wafa, decided to walk the 10-kilometre distance despite the heat and humidity.

“I am so excited that I finally managed to perform the hajj and come to the areas that the Prophet (Mohammed) had once been to,” Wafa said as he walked towards Mina.

From Mina, pilgrims will head to nearby Mount Arafat, where they spend Monday in prayer until sunset.

The oil-rich kingdom has also mobilised huge medical and civil defence resources to ensure the smooth movement of the pilgrims.

The fact that the kingdom accounts for the overwhelming majority of MERS cases reported around the world has raised concerns pilgrims could be infected and return to their homelands carrying the virus.

But authorities have voiced confidence the hajj will pass without incident.

This year's minor pilgrimage season, called the “umrah”, during the fasting month of Ramadan in July-August, passed off without any MERS outbreak even though millions of Muslims took part.

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

Despite being marred by deadly incidents in the past, including floods, stampedes and fires, the hajj has in recent years been almost incident-free, thanks to multi-billion-dollar projects by Saudi authorities.