CAIRO/ISLAMABAD/RIYADH – Extreme heat has proved fatal for hundreds who began the journey last Friday to the Kaaba at the Grand Mosque in Mecca in Saudi Arabia for the annual haj pilgrimage.

Egypt formed a crisis unit on Thursday to investigate the deaths of Egyptians taking part in the annual Muslim pilgrimage to Mecca during extreme heat, after medical and security sources said at least 530 Egyptians had died and 31 were missing.

At least 35 Pakistani citizens died while performing Hajj rituals in different Saudi cities due to extreme weather conditions, Pakistan's Ministry of Religious Affairs and Interfaith Harmony said on Thursday.

READ MORE: Climate threat hangs over haj pilgrimage as hundreds perish in heat

In recent days hundreds of people from different countries have died in punishing conditions for the haj pilgrimage in the Saudi Arabian city, where temperatures have at times exceeded 51 degrees Celsius (124 Fahrenheit).

The haj is mandatory once in a lifetime for every able-bodied Muslim who can afford it and is the most significant manifestation of Islamic faith and unity

Climate scientists have said rising temperatures pose a growing threat to the event, although heat-related deaths along the haj are not new, and have been recorded back to the 1400s.

An Egyptian medical source, who was with the country’s official haj delegation, said the majority of those who died were not formally registered for the event with the authorities, which meant they could not access tents.

In a statement announcing the formation of the crisis unit on the orders of President Abdel Fattah al-Sisi, Egypt's cabinet said 28 deaths had been confirmed from a group of 50,752 officially registered Egyptian pilgrims.

It gave no toll for unregistered pilgrims, saying Egypt was seeking an accurate inventory of the dead and missing and was coordinating with Saudi counterparts to arrange for the transfer of bodies.

Companies that had facilitated travel for unregistered pilgrims would be investigated and penalized, the cabinet added.

A witness said that during the pilgrimage thousands of pilgrims had lain on the streets, exposed to the sun, on the climb to Mount Arafat, which is one of the integral rituals of the journey.

The bodies of dead pilgrims were later covered with Ihram cloth – a simple garb worn by pilgrims – until medical vehicles arrived, the witness said.

The fifth pillar of Islam, the haj is mandatory once in a lifetime for every able-bodied Muslim who can afford it and is the most significant manifestation of Islamic faith and unity. This year's event, which began last Friday, is expected to draw nearly 2 million pilgrims.

According to Pakistan's Ministry of Religious Affairs and Interfaith Harmony, 20 Pakistani haj pilgrims died in Mecca, six in Medina, four in Mina, three in Arafat, and two in Muzdalifah.

READ MORE: 14 Jordanians die during haj in Saudi Arabia, some succumb to heat

"We are notified in case of the death of any pilgrim. The Saudi government has established a system under which permission is sought from the heirs for a regular burial or home return of the deceased,” said Abdul Wahab Soomro, director general of Hajj Mission at the ministry.