More than 1.5 million pilgrims from around the world have amassed in and around Mecca in Saudi Arabia for the Hajj pilgrimage in which the faithful circle the cube-shaped Kaaba in the Grand Mosque, Islam's holiest site.

The number of pilgrims was still growing as more from inside Saudi Arabia joined.

Saudi authorities expected the number of pilgrims to exceed two million this year.

This year’s Hajj came against the backdrop of the raging war in the Gaza between Israel and the Palestinian militant group Hamas, which pushed the entire Middle East to the brink of a regional war between Israel and its allies on one side and Iran and its proxies on the other.

Palestinians in Gaza were not able to travel to Mecca for Hajj this year because of the closure of the Rafah crossing in May when Israel extended its ground offensive to the strip’s southern city of Rafah on the border with Egypt.

Palestinian authorities said 4,200 pilgrims from the occupied West Bank arrived in Mecca for Hajj.

Saudi authorities said 1,000 more from the families of Palestinians killed or wounded in the war in Gaza also arrived to perform Hajj at the invitation of King Salman of Saudi Arabia.

The 1,000 invitees were already outside Gaza — mostly in Egypt — before closure of the Rafah crossing.

The Hajj, one of the world's largest religious gatherings, involves a series of rituals in Mecca and its surroundings in western Saudi Arabia that take several days to complete.

One of the five pillars of Islam, it must be performed at least once by all Muslims who have the means to do so.

After travelling from all parts of the globe to Islam's holiest city, the pilgrims will first perform the "tawaf" -- circling seven times around the Kaaba.

They will then head towards Mina, a valley surrounded by craggy mountains several kilometres outside Mecca, where they will spend the night in air-conditioned tents.

The climax will come on Saturday with day-long prayers on Mount Arafat, where the Prophet Mohammed delivered his final sermon.

Pilgrims in white garments have already been circling the Kaaba in large numbers for several days.

Some have waited for years for the chance to make the trip, with permits allocated by Saudi authorities on a quota basis for each country. (Agencies)