More than two million Muslims begin the annual Haj, one of the world's largest religious gatherings, on Friday.

"All of the arms of state have been deployed (and) we are proud to serve as 'God's hosts'," said security forces spokesperson Bassam Attia.

In total some 2.5 million faithful, the majority from abroad, will undertake the pilgrimage this year, according to local media.

"More than 1.8 million visas were delivered online without the need for middlemen. It's a success," said Haj ministry official Hatim bin Hassan Qadi.

"We feel cleansed by achieving this pillar of Islam and meeting people from across the world. It's marvellous," said Mohamed Jaafar, a 40-year-old Egyptian pilgrim.

"It's an indescribable feeling. You have to live it to understand it," said an Algerian in his fifties completing the pilgrimage for the first time.

"It's a golden opportunity and moment," said his female companion.

Worshippers will participate in weekly prayers late on Friday morning.

During the pilgrimage, men and women will travel to Mina on foot or in buses provided by the authorities.

A district of Makkah, Mina sits in a narrow valley surrounded by rocky mountains and is transformed each year into a vast encampment for pilgrims.

A total of "350,000 air-conditioned tents have been pitched", said a Saudi official.

Worshippers will climb Mount Arafat, also known as the "Mount of Mercy", for hours of prayers and Quran recitals.

After descending, they will gather pebbles and perform the symbolic "stoning of the devil".

That marks the beginning of Eidul Azha, the festival of sacrifice, marked on Sunday in Saudi Arabia and the next day in Pakistan.

Pilgrims then return to the Grand Mosque to perform a final "tawaf" or walk around the Kaaba.

Regional tension

This year's Haj takes place to a backdrop of Gulf tensions following a series of attacks on tankers, the downing of drones and maritime traffic being intercepted.

Riyadh blames regional foe Tehran for the attacks on commercial shipping, accusations Iran vehemently denies.

Despite the absence of diplomatic ties between the two countries, some 88,550 Iranian pilgrims are due to take part in the Haj this year, according to the Tasnim news agency.

As in previous years, Saudi authorities have been at pains to stress that the Haj is a religious event and have sought to prevent its politicisation.

Riyadh claimed its two-year embargo on Doha — which includes restrictions on Qataris travelling to the kingdom — would not affect the pilgrimage.

But Haj official Hassan Qadi acknowledged "very few Qataris have come to Makkah for the pilgrimage".

Saudi's Haj ministry accused Qatar of "politicising the hajj and creating obstacles for Qatari pilgrims", the SPA state news agency reported.

The scale of the pilgrimage presents vast security and logistical challenges, with tens of thousands of safety officers deployed.