Hundreds of thousands of Muslim pilgrims prayed at Mount Arafat in searing heat on Tuesday at the height of an annual hajj pilgrimage held in the fierce Saudi Arabian summer.

Worshippers crowded the rocky rise and surrounding area from before dawn and when the sun appeared, it revealed vast numbers of white-robed worshippers thronging the sacred site.

The ritual is the high point of the annual pilgrimage, one of the five pillars of Islam, that officials say could be the biggest on record after three years of Covid restrictions.

"I'm very happy. It's a moment I have been waiting for my entire life," said Fadia Abdallah, 67, from Egypt, wearing a white abaya and sitting on the ground beneath an umbrella.

High temperatures have been a constant challenge for the pilgrims, who come from around the world, and the mercury hit 44 degrees Celsius (111 degrees Fahrenheit) before midday on the hajj's most physically demanding day.

The hajj has a tragic history of deadly stampedes and fires and as the pilgrims prayed and recited from the Koran, helicopters hovered low overhead, monitoring the crowds.

Tree-shaped water towers sprayed cooling showers on the visitors, and free water bottles and snacks were handed out from large trucks.

Six field hospitals with more than 300 beds have been arranged in Arafat, Yasser Bair, a Saudi defence ministry official, told the state-run Al-Ekhbariya TV.

"I can't believe I'm God's guest," said Rahma, a 57-year-old Libyan housewife, fighting back tears as she spoke.

The hajj is a life goal for many Muslims, who are expected to perform the pilgrimage at least once if they are financially and physically capable.

It is also a big revenue-earner for Saudi Arabia, the world's biggest oil exporter which is trying to pivot its economy towards tourism and inward investment.

- Stoning the devil -

The pilgrims pray all day at Arafat, where the Prophet Mohammed is said to have given his final sermon. After sunset, they will travel the short distance to Muzdalifah, where they will sleep in the open air.

On Wednesday, they will gather pebbles and hurl them at three giant concrete walls in the symbolic "stoning of the devil" ritual.

Then they will return to Mecca's Grand Mosque -- Islam's holiest site -- for a final circumambulation of the Kaaba, the giant black cube that Muslims worldwide pray towards each day.

After three years of Covid restrictions, a record number of more than 2.5 million pilgrims were expected to join this year's hajj, one of the world's largest religious gatherings and a source of legitimacy for Saudi Arabia's royal rulers.

It is the biggest hajj since Saudi authorities scrapped a requirement for women to be accompanied by a male guardian in 2021.

At this year's hajj, which follows the lunar calendar and is not always held in summer, a maximum age limit has also been removed, allowing thousands of elderly to attend.

American engineer Ahmed Ahmadine said he felt "blessed" to be able to take part in the pilgrimage.

"I try to focus on praying for my family and friends," said the 37-year-old.

"This is an opportunity that will not be repeated."