Saudi security forces take part in a military parade in preparation for the annual Haj pilgrimage in the holy city of Makkah on Thursday.

AFP/Makkah

Pilgrims from around the world have begun massing in Saudi Arabia for the Haj, one of the biggest gatherings on the planet, undeterred by a crane collapse that killed 108 people at Islam's holiest site.

More than 1.2mn faithful have already arrived for the annual Haj, which begins on Tuesday against a backdrop of increased jihadi violence, a surge of the deadly Mers virus and with the kingdom at war in Yemen.

From all races and ages, pilgrims flocked into the Grand Mosque, where they prayed - some silently in tears and others loudly in groups carrying their countries' flags.

The Haj is among the five pillars of Islam and every capable Muslim must perform the pilgrimage at least once.

Previously marred by stampedes and fires that killed hundreds, it had been largely incident-free for the past decade after safety improvements.

But on September 11, during severe winds, a construction crane toppled into a courtyard of the Grand Mosque.

Saudis, Iranians, Nigerians, Malaysians, Indonesians and Indians were among the dead.

About 400 more people were injured, but it has not stopped pilgrims carrying out their rituals.

"Do you see the number of people here? Do you think they are fearful? It is quite the opposite. People here have faith in God and perceive those that died as martyrs," said Amin al-Rahman of Bangladesh.

The crane was one of several on a multibillion-dollar expansion to accommodate increasing numbers of faithful.

Million pilgrims

With another million pilgrims expected for the Haj, King Salman acted swiftly to sanction the developer, Saudi Binladin Group.

Samira Abdulwahab, a pilgrim from Sudan who had just finished circling the cube-shaped Kaaba, which all Muslims face to pray, called the Grand Mosque "the safest place in the world".

The Kaaba is now barely visible amid the surrounding construction works.

Tawaf, or circumambulating the Kaaba, is a ritual of the pilgrimage performed by the white-clad pilgrims who come from all over the world.

They are following the 1,400-year-old tradition of Prophet Muhammad.

While the pilgrims will not notice it, they are arriving in a country at war.

Since March, the kingdom has led an Arab coalition conducting air strikes and supporting local forces in Yemen against Shia Houthi rebels.

Hundreds of kilometres south of the Muslim holy cities of Makkah and Medina, at least 61 Saudi soldiers and civilians have been killed since March in shelling and skirmishes on the Saudi frontier with Yemen.

Thousands more people have died inside Yemen.

With Saudi Arabia's rival Iran backing the Houthis, the Yemen war has raised regional tensions.

Tehran and Riyadh also support opposing sides in Syria's civil war, but political differences have not stopped Iran's pilgrims from arriving for Haj.

This year's pilgrimage coincides with a refugee crisis in Europe after millions of asylum seekers, most of them Muslim, fled wars in Syria, Iraq and Afghanistan.

The Islamic State group has seized swathes of Syria and Iraq. It has killed dozens of people this year in bombings at Shia mosques in Saudi Arabia, Yemen and Kuwait.

Mers concern

A challenge again facing the Haj is potential transmission of the deadly Middle East Respiratory Syndrome coronavirus (Mers-CoV).

The capital Riyadh saw a jump in infections last month.

But Health Minister Khaled al-Falih said all pilgrims are so far in "very good, if not excellent health."

Saudi Arabia is the country worst affected by Mers, with 528 deaths since the virus appeared in 2012.

The health ministry has mobilised 25,000 additional medical staff to support the Haj, but says there has never been a case of Mers among pilgrims.

And despite the troubled backdrop, worshippers spoke of their elation at attending an event that marks the peak of their spiritual lives.

"We feel tremendous. We're very, very excited," said Fawzy Abdulrahman, 59, from the Philippines.

"We're praying for our kids," he said, holding his wife's hand and melting into the crowds.