The annual hajj pilgrimage, one of the five pillars of Islam, will start on Saturday with just 60,000 vaccinated Saudi residents allowed to take part this year because of the pandemic.

For the second year in a row, Muslims from abroad have been excluded from the hajj, which drew 2.5 million pilgrims to Saudi Arabia in 2019 before the virus struck.

All Muslims are expected to complete the hajj to Mecca -- from which non-Muslims are strictly banned -- at least once in their lives if they have the means to do so.

Believers converge on the holy city for several days of rituals in which they retrace the Prophet Mohammed's last pilgrimage.

Here is a rundown of the ceremonies at what would usually be one of the largest religious gatherings in the world.

Pilgrims must first enter a state of purity, called ihram, which requires special dress and behaviour.

Men wear a seamless shroud-like white garment that emphasises unity, regardless of social status or nationality.

Women must wear loose dresses, also often white, exposing only their faces and hands.

Pilgrims are not allowed to argue or bicker and are prohibited from wearing perfume, cutting their nails, or trimming their hair or beards.

The first ritual requires walking seven times around the Kaaba, the large black cubic structure at the centre of Mecca's Grand Mosque.

Made from granite and draped in cloth, the Kaaba stands nearly 15 metres (50 feet) tall.

Muslims turn towards the Kaaba to pray, no matter where they are in the world. The structure is said to have been first erected by Adam and then rebuilt by Abraham 4,000 years ago.

The Kaaba is a large black cubic structure at the centre of Mecca's Grand Mosque towards which Muslims turn to pray wherever they are in the world
The Kaaba is a large black cubic structure at the centre of Mecca's Grand Mosque towards which Muslims turn to pray wherever they are in the world AFP / FETHI BELAID

Pilgrims next walk seven times between two stone spots in the mosque.

They then move on to Mina, around five kilometres (three miles) away, ahead of the main rite of the pilgrimage at Mount Arafat.

The climax of the hajj is the gathering on Mount Arafat, about 10 kilometres (six miles) from Mina, where it is believed that the Prophet Mohammed delivered his final sermon.

Pilgrims assemble on the 70-metre-high (230-foot) hill and its surrounding plain for hours of prayers and Koran recitals, staying there until the evening.

After sunset they head to Muzdalifah, halfway between Arafat and Mina, where they gather several dozen pebbles so they can perform the symbolic "stoning of the devil".

The last major ritual of the hajj is back at Mina, where pilgrims throw seven stones at each of three huge concrete walls representing Satan.

The ritual is an emulation of Abraham's stoning of the devil at the three spots where it is said Satan tried to dissuade him from obeying God's order to sacrifice his son, Ishmael.

After the first stoning, the Eid al-Adha feast of sacrifice begins, marking the end of the hajj.

Sheep are slaughtered, in reference to the lamb that God provided for sacrifice instead of Ishmael, in a ceremony that is held at the same time around the world.

Men then shave their heads or trim their hair while women cut a fingertip-length off their locks.

The pilgrims can then change back into normal clothing, returning to circumambulate the Kaaba and complete their stone-throwing rituals before heading home.

The hajj is the last pillar of Islam. The four other essential pillars are: profession of the faith; daily prayers; alms-giving and fasting from dawn to dusk during the holy month of Ramadan.