Mecca (Saudi Arabia): Tens of thousands of vaccinated Muslim pilgrims circled Islam's holiest site in Mecca on Sunday, but remained socially distanced and wore masks as the coronavirus takes its toll on the hajj for a second year running.

The hajj pilgrimage, which once drew some 2.5 million Muslims from all walks of life from across the globe, is now almost unrecognisable. It is being scaled back for the second year in a row due to the coronavirus pandemic.

The pared-down hajj prevents Muslims from outside Saudi Arabia from fulfilling an Islamic obligation and causes financial losses to Saudi Arabia which in pre-pandemic years took in billions of dollars as the custodian of the holy sites.

The Islamic pilgrimage lasts about five days, but traditionally Muslims begin arriving in Mecca weeks ahead of time. The hajj concludes with the Eid al-Adha celebration, marked by the distribution of meat to the poor around the world.

This year, 60,000 vaccinated Saudi citizens or residents of Saudi Arabia have been allowed to perform the hajj due to continued concerns around the spread of the coronavirus. Last year's largely symbolic hajj saw fewer than 1,000 people from within the kingdom taking part.

It's unclear when Saudi Arabia will play host again to millions of Muslims. The kingdom has no clear standard for a vaccine passport, vaccination rates are uneven in different countries and new variants of the virus are threatening the progress already made in some nations.

The kingdom's Al Saud rulers have staked their legitimacy in large part on their custodianship of hajj sites, giving them a unique and powerful platform among Muslims around the world. The kingdom has gone to great lengths to ensure the annual hajj continues uninterrupted, despite changes caused by the pandemic.

Robots have been deployed to spray disinfectant around the cube-shaped Kaaba's busiest walkways. The Kaaba is where the hajj pilgrimage begins and ends for most.

Saudi Arabia is also testing a smart bracelet this year in collaboration with the government's artificial intelligence authority. The touchscreen bracelet resembles the Apple Watch and includes information on the hajj, a pilgrim's oxygen levels and vaccine data and has an emergency feature to call for help.

International media outlets already present in the kingdom were permitted to cover the hajj from Mecca this year, but others were not granted permission to fly in as had been customary before the pandemic.

Cleaners are sanitising the vast white marble spaces of the Grand Mosque that houses the Kaaba several times a day.

We are sanitising the floor and using disinfection liquids while cleaning it two or three times during (each) shift, said Olis Gul, a cleaner who said he has been working in Mecca for 20 years.

The hajj is one of Islam's most important requirements to be performed once in a lifetime. It follows a route the Prophet Muhammad walked nearly 1,400 years ago and is believed to ultimately trace the footsteps of the prophets Ibrahim and Ismail, or Abraham and Ishmael as they are named in the Bible.

The hajj is seen as a chance to wipe clean past sins and bring about greater unity among Muslims. The communal feeling of more than 2 million people from around the world Shiite, Sunni and other Muslim sects praying together, eating together and repenting together has long been part of what makes hajj both a challenging and a transformative experience.

There are questions around whether the hajj will be able to again draw such large numbers of faithful, with male pilgrims forming a sea of white in white terrycloth garments worn to symbolise the equality of mankind before God and women forgoing makeup and perfume to focus inwardly.

Like last year, pilgrims will be drinking water from the holy Zamzam well in plastic bottles. They were given umbrellas to shield them from the sun. They have to carry their own prayer rugs and follow a strict schedule via a mobile app that informs them when they can be in certain areas to avoid crowding.

"I hope this is a successful hajj season," said Egyptian pilgrim Aly Aboulnaga, a university lecturer in Saudi Arabia. We ask God to accept everyone's hajj and for the area to be open to greater numbers of pilgrims and for a return to an even better situation than before.

Prior to the outbreak of COVID-19, the kingdom was working to vastly expand Mecca's ability to host pilgrims with a $60-billion Grand Mosque expansion. On the mosque's south side stands the 1,972-foot (600-metre) clock-tower skyscraper, part of a completed seven-tower complex that was built to accommodate wealthier pilgrims.

The kingdom, with a population of more than 30 million, has reported over half a million cases of the coronavirus, including more than 8,000 deaths. It has administered nearly 20 million doses of coronavirus vaccines, according to the World Health Organisation.