At least 530 Egyptians have died taking part in the haj and another 31 are missing as extreme heat hits the annual Muslim pilgrimage to Makkah, medical and security sources told on Thursday.

Hundreds of people from different countries have died in recent days in punishing conditions at the Saudi Arabian city, where temperatures have at times soared past 51 degrees Celsius (124 Fahrenheit).

The medical source, who was with the official Egyptian Hajj 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.

A Reuters witness said thousands of pilgrims lay on the streets, exposed to the sun, on the climb to Mount Arafat, 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 Hajj 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.

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.

Egyptian authorities have not confirmed the number of deaths.

The foreign ministry and emigration ministry have said they are cooperating with Saudi officials in following up on the search for missing Egyptians and on reports regarding casualties.