Vast crowds of robed Muslim faithful walked solemn circles around the Kaaba, the black cube at Mecca's Grand Mosque on Sunday to begin the biggest hajj pilgrimage in several years, in the heat of the Saudi summer.

Islam's holiest site is expected to host more than two million worshippers from 160 countries during the annual rites that could break attendance records, with 1.6 million foreigners already arriving by late Friday.

"This year, we will witness the largest hajj pilgrimage in history," if things go according to plan, predicted an official with the Saudi Ministry of Hajj and Umrah.

"The numbers will exceed 2.5 million pilgrims," added the official, speaking on condition of anonymity because he is not authorized to speak with the press.

The hajj began early on Sunday with the "tawaf" -– the circumambulation of the Kaaba, the large cubic structure draped in black cloth with gold trimmings that Muslims around the world pray towards every day.

"I am living the most beautiful days of my life," said Saeed Abdel Azim, a 65-year-old Egyptian performing the ritual. "The dream has come true," added the retiree, who had saved for 20 years to pay the thousands of dollars needed to take part.

The hajj is one of the five pillars of Islam and must be undertaken at least once by all Muslims with the means.

A series of rites are completed over four days in Mecca and its surroundings in the west of oil-rich Saudi Arabia.

On Sunday afternoon, pilgrims started moving to Mina, about five kilometers (three miles) from the Grand Mosque, ahead of the hajj's climax at Mount Arafat, where the Prophet Mohammed is believed to have delivered his final sermon.

Mina, the world's largest tent city, readied to receive the influx of pilgrims, with food supplies brought in and security forces deployed around the area.

More worshippers are expected to head to Mina on Monday, as a vibrant atmosphere takes hold of the tented city with the arrival of pilgrims by foot or via air-conditioned buses.

'Great blessing'

Outside the Grand Mosque, thousands prayed on colorful carpets that adorned the pavement, with male pilgrims wearing simple white robes. The area was dotted with ambulances, mobile clinics, and fire trucks.

The hajj poses a considerable security challenge and has seen several disasters over the years, including a 2015 stampede that killed up to 2,300 people.

There have been no major incidents since, and catastrophe was the last thing on pilgrims' minds.

"I cannot describe my feelings," said Indonesian student Yusuf Burhan, 25. "This is a great blessing. I never imagined that I would perform the hajj this year."

This year's summer timing for the hajj, which follows the lunar calendar, is testing the endurance of worshippers during the mostly outdoor ritual.

Carrying white umbrellas to shield themselves from the scorching sun, policemen in the mountainous city have conducted foot patrols and set up checkpoints to inspect hajj permits.

Others splashed water on pilgrims as temperatures climbed towards 45 degrees Celsius (113 degrees Fahrenheit).

Thousands of paramedics were on standby inside the Grand Mosque. Saudi authorities said more than 32,000 health workers will be on hand to treat cases of heatstroke, dehydration, and exhaustion.

'Not a single vacant bed'

The hajj, which costs at least $5,000 a person, makes billions of dollars a year for Saudi Arabia, the world's biggest oil exporter, which is trying to diversify its economy beyond fossil fuels.

This year's will be the biggest since 2019, before the Covid pandemic, when about 2.5 million people took part.

Only 10,000 were allowed in 2020, at the height of the global outbreak, rising to nearly 59,000 in 2021.

Last year's cap of one million has been removed.

Saudi businessman Samir al-Zafni said all his hotels in Mecca and Madinah are at full capacity until the first week of July.

"This year there is not a single vacant bed in our group of 67 hotels," he told AFP.

The hajj also demonstrates social reforms in the deeply conservative kingdom.

This year's pilgrimage will be the biggest since Saudi Arabia scrapped rules in 2021 that banned women who weren't accompanied by a male relative.

Waiting for a car to take him out of the vicinity of Mecca's grand mosque, Moroccan merchant Abdullah al-Haqouni, 65, said he was struggling with the temperature.

"I am very tired. The heat is unbearable," he said, carrying a green umbrella. "God help us."